Initial commit: Lagerbestand Blazor Projekt

Lagerbestand/Models/AppUser.cs

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+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+public enum UserRole
+{
+    User = 0,
+    Worker = 1,  // Changed from Owner - limited access to tire operations and inventory
+    Admin = 2    // Full access to everything
+}
+
+public class AppUser
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(100)]
+    public string Username { get; set; } = string.Empty;
+
+    [Required]
+    [MaxLength(256)]
+    public string PasswordHash { get; set; } = string.Empty;
+
+    [MaxLength(200)]
+    public string? DisplayName { get; set; }
+
+    public UserRole Role { get; set; } = UserRole.User;
+
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? LastLoginAt { get; set; }
+
+    /// <summary>
+    /// Whether 2FA is enabled for this user (user opted in or admin enforced).
+    /// </summary>
+    public bool TwoFactorEnabled { get; set; }
+
+    /// <summary>
+    /// Base32-encoded TOTP secret key for authenticator apps.
+    /// </summary>
+    [MaxLength(256)]
+    public string? TwoFactorSecret { get; set; }
+
+    /// <summary>
+    /// Whether an admin has enforced 2FA for this user.
+    /// When true, the user cannot disable 2FA themselves.
+    /// </summary>
+    public bool TwoFactorEnforced { get; set; }
+}

Lagerbestand/Models/AreaType.cs

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+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents the storage area type for tire storage locations.
+/// The value corresponds to position A in the location code (ABCD format).
+/// </summary>
+public enum AreaType
+{
+    /// <summary>
+    /// Werkstatt (Gebäude 1, 3 Regalreihen) - Code prefix: 1
+    /// </summary>
+    Werkstatt = 1,
+
+    /// <summary>
+    /// Lager (Gebäude 2, 5 Regalreihen) - Code prefix: 2
+    /// </summary>
+    Lager = 2
+}
+
+/// <summary>
+/// Extension methods for AreaType enum.
+/// </summary>
+public static class AreaTypeExtensions
+{
+    /// <summary>
+    /// Gets the German display name for the area type.
+    /// </summary>
+    public static string GetDisplayName(this AreaType areaType) => areaType switch
+    {
+        AreaType.Lager => "Lager",
+        AreaType.Werkstatt => "Werkstatt",
+        _ => areaType.ToString()
+    };
+
+    /// <summary>
+    /// Gets the single-digit code for the area type.
+    /// </summary>
+    public static string GetCode(this AreaType areaType) => ((int)areaType).ToString();
+
+    /// <summary>
+    /// Gets the maximum shelf row number for the building.
+    /// Werkstatt (Gebäude 1) has 3 rows, Lager (Gebäude 2) has 5 rows.
+    /// </summary>
+    public static int GetMaxRow(this AreaType areaType) => areaType switch
+    {
+        AreaType.Werkstatt => 3,
+        AreaType.Lager => 5,
+        _ => 1
+    };
+
+    /// <summary>
+    /// Gets a display label including the building number (e.g., "Gebäude 1 – Werkstatt").
+    /// </summary>
+    public static string GetBuildingLabel(this AreaType areaType) =>
+        $"Gebäude {(int)areaType} – {areaType.GetDisplayName()}";
+
+    /// <summary>
+    /// Parses a code digit to AreaType.
+    /// </summary>
+    /// <param name="code">Single digit code (1 or 2)</param>
+    /// <returns>The corresponding AreaType</returns>
+    /// <exception cref="ArgumentException">If code is not valid</exception>
+    public static AreaType FromCode(char code) => code switch
+    {
+        '1' => AreaType.Werkstatt,
+        '2' => AreaType.Lager,
+        _ => throw new ArgumentException($"Ungültiger Bereichscode: {code}. Erlaubt: 1 (Werkstatt), 2 (Lager)", nameof(code))
+    };
+
+    /// <summary>
+    /// Tries to parse a code digit to AreaType.
+    /// </summary>
+    public static bool TryFromCode(char code, out AreaType areaType)
+    {
+        areaType = default;
+        if (code == '1')
+        {
+            areaType = AreaType.Werkstatt;
+            return true;
+        }
+        if (code == '2')
+        {
+            areaType = AreaType.Lager;
+            return true;
+        }
+        return false;
+    }
+}

Lagerbestand/Models/CatalogItem.cs

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+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Type of catalog item
+/// </summary>
+public enum CatalogItemType
+{
+    /// <summary>
+    /// Tire category
+    /// </summary>
+    Reifen = 0,
+
+    /// <summary>
+    /// Rim/wheel category
+    /// </summary>
+    Felgen = 1
+}
+
+public class CatalogItem
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(200)]
+    public string Name { get; set; } = string.Empty;
+
+    [MaxLength(500)]
+    public string? PictureFileName { get; set; }
+
+    /// <summary>
+    /// Size info - tire size for Reifen (e.g., "225/45 R17"), rim size for Felgen (e.g., "17 Zoll")
+    /// </summary>
+    [MaxLength(50)]
+    public string TireSize { get; set; } = string.Empty;
+
+    public TireSeason Season { get; set; } = TireSeason.Sommer;
+
+    /// <summary>
+    /// Category type (Reifen or Felgen)
+    /// </summary>
+    public CatalogItemType Type { get; set; } = CatalogItemType.Reifen;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>
+    /// Display label for the size field based on type
+    /// </summary>
+    [NotMapped]
+    public string SizeLabel => Type == CatalogItemType.Felgen ? "Felgengröße" : "Reifengröße";
+
+    /// <summary>
+    /// Display details string
+    /// </summary>
+    [NotMapped]
+    public string DisplayDetails => Type == CatalogItemType.Felgen
+        ? TireSize
+        : $"{TireSize} | {Season}";
+}
+
+public enum TireSeason
+{
+    Sommer = 0,
+    Winter = 1,
+    Allrad = 2
+}

Lagerbestand/Models/Customer.cs

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+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a customer who stores tires at the shop.
+/// A customer can have multiple vehicles.
+/// </summary>
+public class Customer
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [MaxLength(100)]
+    public string? FirstName { get; set; }
+
+    [Required]
+    [MaxLength(100)]
+    public string LastName { get; set; } = string.Empty;
+
+    [MaxLength(200)]
+    public string? Company { get; set; }
+
+    [MaxLength(20)]
+    public string? Phone { get; set; }
+
+    [MaxLength(100)]
+    public string? Email { get; set; }
+
+    [MaxLength(500)]
+    public string? Notes { get; set; }
+
+    /// <summary>
+    /// Customer number for easy identification (e.g., K-0001)
+    /// </summary>
+    [MaxLength(20)]
+    public string CustomerNumber { get; set; } = string.Empty;
+
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>
+    /// Navigation property for customer's vehicles
+    /// </summary>
+    public ICollection<Vehicle> Vehicles { get; set; } = new List<Vehicle>();
+
+    /// <summary>
+    /// Navigation property for customer's stored tire stacks
+    /// </summary>
+    public ICollection<TireStack> TireStacks { get; set; } = new List<TireStack>();
+
+    /// <summary>
+    /// Full name of the customer
+    /// </summary>
+    [NotMapped]
+    public string FullName => $"{FirstName} {LastName}".Trim();
+
+    /// <summary>
+    /// Display name including company if available
+    /// </summary>
+    [NotMapped]
+    public string DisplayName => string.IsNullOrEmpty(Company) 
+        ? FullName 
+        : $"{FullName} ({Company})";
+
+    /// <summary>
+    /// Gets the primary vehicle or the first vehicle if no primary is set
+    /// </summary>
+    [NotMapped]
+    public Vehicle? PrimaryVehicle => Vehicles
+        .Where(v => v.IsActive)
+        .OrderByDescending(v => v.IsPrimary)
+        .ThenBy(v => v.CreatedAt)
+        .FirstOrDefault();
+
+    /// <summary>
+    /// Gets all active vehicles for this customer
+    /// </summary>
+    [NotMapped]
+    public IEnumerable<Vehicle> ActiveVehicles => Vehicles.Where(v => v.IsActive);
+
+    }

Lagerbestand/Models/FileStorageSettings.cs

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+namespace Lagerbestand.Models;
+
+/// <summary>
+/// File storage settings for NFS/disk-based file storage
+/// </summary>
+public class FileStorageSettings
+{
+    /// <summary>
+    /// Base path for file storage (e.g., /mnt/nfs/attachments or C:\Storage\Attachments)
+    /// </summary>
+    public string BasePath { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Whether file storage is configured and enabled
+    /// </summary>
+    public bool IsEnabled { get; set; }
+
+    /// <summary>
+    /// Maximum file size in bytes (default: 10 MB)
+    /// </summary>
+    public long MaxFileSizeBytes { get; set; } = 10 * 1024 * 1024;
+
+    /// <summary>
+    /// Validates if the storage path is accessible
+    /// </summary>
+    public bool IsPathAccessible()
+    {
+        if (string.IsNullOrWhiteSpace(BasePath))
+            return false;
+
+        try
+        {
+            return Directory.Exists(BasePath);
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
+    /// <summary>
+    /// Gets the full path for a given relative file path
+    /// </summary>
+    public string GetFullPath(string relativePath)
+    {
+        return Path.Combine(BasePath, relativePath);
+    }
+}

Lagerbestand/Models/InventoryItem.cs

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+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+public class InventoryItem
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(500)]
+    public string QrCode { get; set; } = string.Empty;
+
+    [MaxLength(200)]
+    public string? Name { get; set; }
+
+    [MaxLength(500)]
+    public string? Description { get; set; }
+
+    public Guid? CatalogItemId { get; set; }
+
+    [ForeignKey(nameof(CatalogItemId))]
+    public CatalogItem? CatalogItem { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+}

Lagerbestand/Models/KanbanColumn.cs

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+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a column in the Kanban board (e.g., Backlog, ToDo, In Progress)
+/// </summary>
+public class KanbanColumn
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(100)]
+    public string Name { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Display order of the column (0-based)
+    /// </summary>
+    public int SortOrder { get; set; }
+
+    /// <summary>
+    /// Optional color for the column header
+    /// </summary>
+    [MaxLength(7)]
+    public string? Color { get; set; }
+
+    /// <summary>
+    /// Optional icon/emoji for the column
+    /// </summary>
+    [MaxLength(10)]
+    public string? Icon { get; set; }
+
+    /// <summary>
+    /// Whether this is the default column for new tasks
+    /// </summary>
+    public bool IsDefault { get; set; }
+
+    /// <summary>
+    /// Whether this column represents completed tasks (for archiving logic)
+    /// </summary>
+    public bool IsCompletedColumn { get; set; }
+
+    /// <summary>
+    /// Whether this column is active
+    /// </summary>
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual ICollection<KanbanTask> Tasks { get; set; } = new List<KanbanTask>();
+}

Lagerbestand/Models/KanbanLabel.cs

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+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a label that can be attached to Kanban tasks
+/// </summary>
+public class KanbanLabel
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(50)]
+    public string Name { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Hex color code for the label (e.g., "#FF5733")
+    /// </summary>
+    [Required]
+    [MaxLength(7)]
+    public string Color { get; set; } = "#6B7280";
+
+    /// <summary>
+    /// Optional description for the label
+    /// </summary>
+    [MaxLength(200)]
+    public string? Description { get; set; }
+
+    /// <summary>
+    /// Display order for labels
+    /// </summary>
+    public int SortOrder { get; set; }
+
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual ICollection<KanbanTaskLabel> TaskLabels { get; set; } = new List<KanbanTaskLabel>();
+    public virtual ICollection<KanbanTaskTemplateLabel> TemplateLabels { get; set; } = new List<KanbanTaskTemplateLabel>();
+}
+
+/// <summary>
+/// Predefined label colors for easy selection
+/// </summary>
+public static class KanbanLabelColors
+{
+    public static readonly Dictionary<string, string> Presets = new()
+    {
+        { "Rot", "#EF4444" },
+        { "Orange", "#F97316" },
+        { "Gelb", "#EAB308" },
+        { "Grün", "#22C55E" },
+        { "Türkis", "#14B8A6" },
+        { "Blau", "#3B82F6" },
+        { "Indigo", "#6366F1" },
+        { "Violett", "#8B5CF6" },
+        { "Pink", "#EC4899" },
+        { "Grau", "#6B7280" }
+    };
+}

Lagerbestand/Models/KanbanStatistics.cs

@@ -0,0 +1,32 @@
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Statistics for the Kanban dashboard
+/// </summary>
+public class KanbanStatistics
+{
+    /// <summary>
+    /// Total number of non-archived tasks
+    /// </summary>
+    public int TotalTasks { get; set; }
+
+    /// <summary>
+    /// Number of tasks due today
+    /// </summary>
+    public int TasksDueToday { get; set; }
+
+    /// <summary>
+    /// Number of overdue tasks
+    /// </summary>
+    public int OverdueTasks { get; set; }
+
+    /// <summary>
+    /// Number of tasks completed this week
+    /// </summary>
+    public int CompletedThisWeek { get; set; }
+
+    /// <summary>
+    /// Count of tasks per column
+    /// </summary>
+    public Dictionary<Guid, int> TasksPerColumn { get; set; } = new();
+}

Lagerbestand/Models/KanbanTask.cs

@@ -0,0 +1,141 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Priority levels for Kanban tasks
+/// </summary>
+public enum KanbanTaskPriority
+{
+    Low = 0,
+    Medium = 1,
+    High = 2,
+    Urgent = 3
+}
+
+/// <summary>
+/// Represents a task/card in the Kanban board
+/// </summary>
+public class KanbanTask
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(200)]
+    public string Title { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Rich text description of the task
+    /// </summary>
+    public string? Description { get; set; }
+
+    /// <summary>
+    /// The column this task belongs to
+    /// </summary>
+    public Guid ColumnId { get; set; }
+
+    /// <summary>
+    /// Sort order within the column
+    /// </summary>
+    public int SortOrder { get; set; }
+
+    /// <summary>
+    /// Due date for the task
+    /// </summary>
+    public DateTime? DueDate { get; set; }
+
+    /// <summary>
+    /// Priority level
+    /// </summary>
+    public KanbanTaskPriority Priority { get; set; } = KanbanTaskPriority.Medium;
+
+    /// <summary>
+    /// Estimated time in minutes
+    /// </summary>
+    public int? EstimatedMinutes { get; set; }
+
+    /// <summary>
+    /// User who created the task
+    /// </summary>
+    public Guid? CreatedByUserId { get; set; }
+
+    /// <summary>
+    /// Whether the task is archived
+    /// </summary>
+    public bool IsArchived { get; set; }
+
+    /// <summary>
+    /// When the task was moved to a completed column
+    /// </summary>
+    public DateTime? CompletedAt { get; set; }
+
+    /// <summary>
+    /// When the task was archived
+    /// </summary>
+    public DateTime? ArchivedAt { get; set; }
+
+    /// <summary>
+    /// Simple notes/memo field for the task
+    /// </summary>
+    public string? NotesText { get; set; }
+
+    /// <summary>
+    /// Free text field for tire size notes (Reifengröße)
+    /// </summary>
+    public string? TireSizeNote { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual KanbanColumn? Column { get; set; }
+    public virtual AppUser? CreatedByUser { get; set; }
+
+    public virtual ICollection<KanbanTaskTodo> Todos { get; set; } = new List<KanbanTaskTodo>();
+    public virtual ICollection<KanbanTaskLabel> TaskLabels { get; set; } = new List<KanbanTaskLabel>();
+    public virtual ICollection<KanbanTaskComment> Comments { get; set; } = new List<KanbanTaskComment>();
+    public virtual ICollection<KanbanTaskNote> Notes { get; set; } = new List<KanbanTaskNote>();
+    public virtual ICollection<KanbanTaskAttachment> Attachments { get; set; } = new List<KanbanTaskAttachment>();
+    public virtual ICollection<KanbanTaskAssignee> Assignees { get; set; } = new List<KanbanTaskAssignee>();
+    public virtual ICollection<KanbanTaskCustomer> TaskCustomers { get; set; } = new List<KanbanTaskCustomer>();
+    public virtual ICollection<KanbanTaskTireStack> TaskTireStacks { get; set; } = new List<KanbanTaskTireStack>();
+
+    // Computed properties
+    public bool IsDueToday => DueDate.HasValue && DueDate.Value.Date == DateTime.UtcNow.Date && !CompletedAt.HasValue;
+    public bool IsOverdue => DueDate.HasValue && DueDate.Value.Date < DateTime.UtcNow.Date && !IsArchived && !CompletedAt.HasValue;
+
+    public int TodosCompleted => Todos.Count(t => t.IsCompleted);
+    public int TodosTotal => Todos.Count;
+    public string TodoProgress => TodosTotal > 0 ? $"{TodosCompleted}/{TodosTotal}" : "";
+
+    public string PriorityText => Priority switch
+    {
+        KanbanTaskPriority.Low => "Niedrig",
+        KanbanTaskPriority.Medium => "Mittel",
+        KanbanTaskPriority.High => "Hoch",
+        KanbanTaskPriority.Urgent => "Dringend",
+        _ => "Mittel"
+    };
+
+    public string PriorityIcon => Priority switch
+    {
+        KanbanTaskPriority.Low => "⬇️",
+        KanbanTaskPriority.Medium => "➡️",
+        KanbanTaskPriority.High => "⬆️",
+        KanbanTaskPriority.Urgent => "🔥",
+        _ => "➡️"
+    };
+
+    public string EstimatedTimeDisplay
+    {
+        get
+        {
+            if (!EstimatedMinutes.HasValue) return "";
+            var hours = EstimatedMinutes.Value / 60;
+            var mins = EstimatedMinutes.Value % 60;
+            if (hours > 0 && mins > 0) return $"{hours}h {mins}m";
+            if (hours > 0) return $"{hours}h";
+            return $"{mins}m";
+        }
+    }
+}

Lagerbestand/Models/KanbanTaskAttachment.cs

@@ -0,0 +1,96 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a file attachment on a Kanban task
+/// </summary>
+public class KanbanTaskAttachment
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    public Guid TaskId { get; set; }
+
+    [Required]
+    [MaxLength(255)]
+    public string FileName { get; set; } = string.Empty;
+
+    [Required]
+    [MaxLength(100)]
+    public string ContentType { get; set; } = "application/octet-stream";
+
+    /// <summary>
+    /// File size in bytes
+    /// </summary>
+    public long FileSize { get; set; }
+
+    /// <summary>
+    /// Relative path to the file in the storage system (NFS/disk)
+    /// </summary>
+    [MaxLength(500)]
+    public string? FilePath { get; set; }
+
+    /// <summary>
+    /// Legacy: File content stored as binary (being migrated to file-based storage)
+    /// </summary>
+    [Obsolete("Use FilePath instead. This property is retained for migration purposes only.")]
+    public byte[]? FileContent { get; set; }
+
+    /// <summary>
+    /// User who uploaded the file
+    /// </summary>
+    public Guid? UploadedByUserId { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual AppUser? UploadedByUser { get; set; }
+
+    // Computed properties
+    [NotMapped]
+    public string FileSizeDisplay
+    {
+        get
+        {
+            if (FileSize < 1024) return $"{FileSize} B";
+            if (FileSize < 1024 * 1024) return $"{FileSize / 1024.0:F1} KB";
+            return $"{FileSize / (1024.0 * 1024.0):F1} MB";
+        }
+    }
+
+    [NotMapped]
+    public string FileIcon
+    {
+        get
+        {
+            var ext = Path.GetExtension(FileName).ToLowerInvariant();
+            return ext switch
+            {
+                ".pdf" => "📄",
+                ".doc" or ".docx" => "📝",
+                ".xls" or ".xlsx" => "📊",
+                ".ppt" or ".pptx" => "📽️",
+                ".jpg" or ".jpeg" or ".png" or ".gif" or ".webp" => "🖼️",
+                ".zip" or ".rar" or ".7z" => "📦",
+                ".txt" => "📃",
+                _ => "📎"
+            };
+        }
+    }
+
+    [NotMapped]
+    public bool IsImage => ContentType.StartsWith("image/");
+
+    /// <summary>
+    /// Whether the file is stored on disk (vs legacy database storage)
+    /// </summary>
+    [NotMapped]
+    public bool IsFileBasedStorage => !string.IsNullOrEmpty(FilePath);
+
+    /// <summary>
+    /// Maximum file size allowed (10 MB)
+    /// </summary>
+    public const long MaxFileSize = 10 * 1024 * 1024;
+}

Lagerbestand/Models/KanbanTaskComment.cs

@@ -0,0 +1,45 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Type of comment (chat message or system activity)
+/// </summary>
+public enum KanbanCommentType
+{
+    Chat = 0,
+    Activity = 1
+}
+
+/// <summary>
+/// Represents a chat message or activity log entry on a Kanban task
+/// </summary>
+public class KanbanTaskComment
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    public Guid TaskId { get; set; }
+
+    /// <summary>
+    /// User who created the comment (null for system activities)
+    /// </summary>
+    public Guid? UserId { get; set; }
+
+    [Required]
+    public string Content { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Whether this is a chat message or system activity
+    /// </summary>
+    public KanbanCommentType CommentType { get; set; } = KanbanCommentType.Chat;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual AppUser? User { get; set; }
+
+    // Computed properties
+    public bool IsActivity => CommentType == KanbanCommentType.Activity;
+    public bool IsChat => CommentType == KanbanCommentType.Chat;
+}

Lagerbestand/Models/KanbanTaskNote.cs

@@ -0,0 +1,36 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a shared editable note on a Kanban task (like MS Teams wiki)
+/// </summary>
+public class KanbanTaskNote
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    public Guid TaskId { get; set; }
+
+    [Required]
+    [MaxLength(100)]
+    public string Title { get; set; } = "Notizen";
+
+    /// <summary>
+    /// Rich text content of the note
+    /// </summary>
+    public string Content { get; set; } = string.Empty;
+
+    public int SortOrder { get; set; }
+
+    /// <summary>
+    /// Last user who edited the note
+    /// </summary>
+    public Guid? LastEditedByUserId { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual AppUser? LastEditedByUser { get; set; }
+}

Lagerbestand/Models/KanbanTaskRelations.cs

@@ -0,0 +1,57 @@
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Many-to-many relationship between KanbanTask and KanbanLabel
+/// </summary>
+public class KanbanTaskLabel
+{
+    public Guid TaskId { get; set; }
+    public Guid LabelId { get; set; }
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual KanbanLabel? Label { get; set; }
+}
+
+/// <summary>
+/// Many-to-many relationship between KanbanTask and User (assignees)
+/// </summary>
+public class KanbanTaskAssignee
+{
+    public Guid TaskId { get; set; }
+    public Guid UserId { get; set; }
+
+    public DateTime AssignedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual AppUser? User { get; set; }
+}
+
+/// <summary>
+/// Many-to-many relationship between KanbanTask and Customer
+/// </summary>
+public class KanbanTaskCustomer
+{
+    public Guid TaskId { get; set; }
+    public Guid CustomerId { get; set; }
+    public Guid? VehicleId { get; set; }
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual Customer? Customer { get; set; }
+    public virtual Vehicle? Vehicle { get; set; }
+}
+
+/// <summary>
+/// Many-to-many relationship between KanbanTask and TireStack
+/// </summary>
+public class KanbanTaskTireStack
+{
+    public Guid TaskId { get; set; }
+    public Guid TireStackId { get; set; }
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+    public virtual TireStack? TireStack { get; set; }
+}

Lagerbestand/Models/KanbanTaskTemplate.cs

@@ -0,0 +1,92 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a task template that can be used to quickly create new tasks
+/// </summary>
+public class KanbanTaskTemplate
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    [MaxLength(100)]
+    public string Name { get; set; } = string.Empty;
+
+    [MaxLength(500)]
+    public string? Description { get; set; }
+
+    /// <summary>
+    /// Title pattern for tasks created from this template
+    /// Can include placeholders like {Kunde}
+    /// </summary>
+    [MaxLength(200)]
+    public string TitlePattern { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Default description for tasks
+    /// </summary>
+    public string? DefaultDescription { get; set; }
+
+    /// <summary>
+    /// Default column for tasks created from this template
+    /// </summary>
+    public Guid? DefaultColumnId { get; set; }
+
+    /// <summary>
+    /// Default priority for tasks
+    /// </summary>
+    public KanbanTaskPriority DefaultPriority { get; set; } = KanbanTaskPriority.Medium;
+
+    /// <summary>
+    /// Default estimated minutes
+    /// </summary>
+    public int? DefaultEstimatedMinutes { get; set; }
+
+    /// <summary>
+    /// Display order for templates
+    /// </summary>
+    public int SortOrder { get; set; }
+
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+
+    // Navigation properties
+    public virtual KanbanColumn? DefaultColumn { get; set; }
+    public virtual ICollection<KanbanTaskTemplateTodo> Todos { get; set; } = new List<KanbanTaskTemplateTodo>();
+    public virtual ICollection<KanbanTaskTemplateLabel> TemplateLabels { get; set; } = new List<KanbanTaskTemplateLabel>();
+}
+
+/// <summary>
+/// Predefined todo item for a template
+/// </summary>
+public class KanbanTaskTemplateTodo
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    public Guid TemplateId { get; set; }
+
+    [Required]
+    [MaxLength(500)]
+    public string Text { get; set; } = string.Empty;
+
+    public int SortOrder { get; set; }
+
+    // Navigation properties
+    public virtual KanbanTaskTemplate? Template { get; set; }
+}
+
+/// <summary>
+/// Default label for a template (many-to-many)
+/// </summary>
+public class KanbanTaskTemplateLabel
+{
+    public Guid TemplateId { get; set; }
+    public Guid LabelId { get; set; }
+
+    // Navigation properties
+    public virtual KanbanTaskTemplate? Template { get; set; }
+    public virtual KanbanLabel? Label { get; set; }
+}

Lagerbestand/Models/KanbanTaskTodo.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a todo/checklist item within a Kanban task
+/// </summary>
+public class KanbanTaskTodo
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    public Guid TaskId { get; set; }
+
+    [Required]
+    [MaxLength(500)]
+    public string Text { get; set; } = string.Empty;
+
+    public bool IsCompleted { get; set; }
+
+    public int SortOrder { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime? CompletedAt { get; set; }
+
+    // Navigation properties
+    public virtual KanbanTask? Task { get; set; }
+}

Lagerbestand/Models/ShelfPosition.cs

@@ -0,0 +1,113 @@
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents the position within a shelf slot (side + level).
+/// The value corresponds to position C in the location code (ABCD format).
+/// </summary>
+public enum ShelfPosition
+{
+    /// <summary>
+    /// Links oben - Code: 1
+    /// </summary>
+    LinksOben = 1,
+
+    /// <summary>
+    /// Links unten - Code: 2
+    /// </summary>
+    LinksUnten = 2,
+
+    /// <summary>
+    /// Rechts oben - Code: 3
+    /// </summary>
+    RechtsOben = 3,
+
+    /// <summary>
+    /// Rechts unten - Code: 4
+    /// </summary>
+    RechtsUnten = 4
+}
+
+/// <summary>
+/// Extension methods for ShelfPosition enum.
+/// </summary>
+public static class ShelfPositionExtensions
+{
+    /// <summary>
+    /// Gets the German display name for the shelf position.
+    /// </summary>
+    public static string GetDisplayName(this ShelfPosition position) => position switch
+    {
+        ShelfPosition.LinksOben => "Links oben",
+        ShelfPosition.LinksUnten => "Links unten",
+        ShelfPosition.RechtsOben => "Rechts oben",
+        ShelfPosition.RechtsUnten => "Rechts unten",
+        _ => position.ToString()
+    };
+
+    /// <summary>
+    /// Gets a short display name (e.g., "L↑") for compact grid views.
+    /// </summary>
+    public static string GetShortName(this ShelfPosition position) => position switch
+    {
+        ShelfPosition.LinksOben => "L↑",
+        ShelfPosition.LinksUnten => "L↓",
+        ShelfPosition.RechtsOben => "R↑",
+        ShelfPosition.RechtsUnten => "R↓",
+        _ => position.ToString()
+    };
+
+    /// <summary>
+    /// Whether the position is on the left side of the shelf.
+    /// </summary>
+    public static bool IsLeft(this ShelfPosition position) =>
+        position is ShelfPosition.LinksOben or ShelfPosition.LinksUnten;
+
+    /// <summary>
+    /// Whether the position is on the top level of the shelf.
+    /// </summary>
+    public static bool IsTop(this ShelfPosition position) =>
+        position is ShelfPosition.LinksOben or ShelfPosition.RechtsOben;
+
+    /// <summary>
+    /// Gets the single-digit code for the position.
+    /// </summary>
+    public static string GetCode(this ShelfPosition position) => ((int)position).ToString();
+
+    /// <summary>
+    /// Parses a code digit to ShelfPosition.
+    /// </summary>
+    /// <param name="code">Single digit code (1-4)</param>
+    /// <exception cref="ArgumentException">If code is not valid</exception>
+    public static ShelfPosition FromCode(char code) => code switch
+    {
+        '1' => ShelfPosition.LinksOben,
+        '2' => ShelfPosition.LinksUnten,
+        '3' => ShelfPosition.RechtsOben,
+        '4' => ShelfPosition.RechtsUnten,
+        _ => throw new ArgumentException($"Ungültiger Positionscode: {code}. Erlaubt: 1-4", nameof(code))
+    };
+
+    /// <summary>
+    /// Tries to parse a code digit to ShelfPosition.
+    /// </summary>
+    public static bool TryFromCode(char code, out ShelfPosition position)
+    {
+        position = default;
+        if (code is < '1' or > '4')
+            return false;
+
+        position = (ShelfPosition)(code - '0');
+        return true;
+    }
+
+    /// <summary>
+    /// All shelf positions in display order.
+    /// </summary>
+    public static readonly ShelfPosition[] All =
+    [
+        ShelfPosition.LinksOben,
+        ShelfPosition.LinksUnten,
+        ShelfPosition.RechtsOben,
+        ShelfPosition.RechtsUnten
+    ];
+}

Lagerbestand/Models/SiteSettings.cs

@@ -0,0 +1,189 @@
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Site-wide settings stored in the database
+/// </summary>
+public class SiteSettings
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+    
+    /// <summary>
+    /// Unique key for the setting (e.g., "PromoBanner")
+    /// </summary>
+    public string Key { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// JSON-serialized value of the setting
+    /// </summary>
+    public string Value { get; set; } = string.Empty;
+    
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime? UpdatedAt { get; set; }
+}
+
+/// <summary>
+/// Promotion banner settings
+/// </summary>
+public class PromoBannerSettings
+{
+    public bool IsEnabled { get; set; }
+    public string Title { get; set; } = string.Empty;
+    public string Message { get; set; } = string.Empty;
+    public DateTime? StartDate { get; set; }
+    public DateTime? EndDate { get; set; }
+    public bool ShowContactButton { get; set; } = true;
+    
+    /// <summary>
+    /// Check if banner should be shown based on current date and content
+    /// </summary>
+    public bool ShouldShow()
+    {
+        // Must be enabled
+        if (!IsEnabled) return false;
+
+        // Must have content
+        if (string.IsNullOrWhiteSpace(Title) && string.IsNullOrWhiteSpace(Message))
+            return false;
+
+        var now = DateTime.UtcNow.Date;
+
+        // Check date range if specified
+        if (StartDate.HasValue && now < StartDate.Value.Date)
+            return false;
+
+        if (EndDate.HasValue && now > EndDate.Value.Date)
+            return false;
+
+        return true;
+    }
+}
+
+/// <summary>
+/// Lexware API connection settings for customer data synchronization
+/// </summary>
+public class LexwareApiSettings
+{
+    public bool IsEnabled { get; set; }
+
+    /// <summary>
+    /// Lexware API base URL (e.g., https://api.lexoffice.io/v1)
+    /// </summary>
+    public string BaseUrl { get; set; } = string.Empty;
+
+    /// <summary>
+    /// API key for authentication
+    /// </summary>
+    public string ApiKey { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Whether automatic daily sync is enabled
+    /// </summary>
+    public bool AutoSyncEnabled { get; set; } = true;
+
+    /// <summary>
+    /// Time of day for automatic sync (HH:mm format)
+    /// </summary>
+    public string AutoSyncTime { get; set; } = "02:00";
+
+    /// <summary>
+    /// Timestamp of the last successful sync
+    /// </summary>
+    public DateTime? LastSyncAt { get; set; }
+
+    /// <summary>
+    /// Result message from the last sync
+    /// </summary>
+    public string? LastSyncResult { get; set; }
+
+    /// <summary>
+    /// Number of customers synced in last run
+    /// </summary>
+    public int LastSyncCount { get; set; }
+
+    /// <summary>
+    /// Whether the API connection is configured
+    /// </summary>
+    public bool IsConfigured => !string.IsNullOrWhiteSpace(BaseUrl) && !string.IsNullOrWhiteSpace(ApiKey);
+}
+
+/// <summary>
+/// Two-Factor Authentication settings stored in SiteSettings
+/// </summary>
+public class TwoFactorSettings
+{
+    /// <summary>
+    /// Global toggle: when false, no 2FA is used at all
+    /// </summary>
+    public bool IsEnabled { get; set; }
+
+    /// <summary>
+    /// Issuer name shown in authenticator apps (e.g. "Reifen Späth")
+    /// </summary>
+    public string Issuer { get; set; } = "Reifen Späth Lagerverwaltung";
+
+    /// <summary>
+    /// Whether email fallback codes are enabled
+    /// </summary>
+    public bool EmailFallbackEnabled { get; set; }
+}
+
+/// <summary>
+/// Session / long-duration usage settings (idle lock, circuit retention).
+/// Editable by admins in the Status page.
+/// </summary>
+public class SessionSettings
+{
+    public const int DefaultIdleTimeoutMinutes = 60;
+    public const int MaxIdleTimeoutMinutes = 60;
+    public const int MinIdleTimeoutMinutes = 1;
+
+    public const double DefaultCircuitRetentionHours = 2.0;
+    public const double MaxCircuitRetentionHours = 4.0;
+    public const double MinCircuitRetentionHours = 0.5;
+
+    /// <summary>
+    /// Minutes of inactivity before the browser tab shows a "Confirm to continue" lock overlay.
+    /// Range: 1 – 60. Default: 60.
+    /// </summary>
+    public int IdleTimeoutMinutes { get; set; } = DefaultIdleTimeoutMinutes;
+
+    /// <summary>
+    /// Hours a disconnected Blazor Server circuit is retained on the server
+    /// before being discarded (allows reconnect without state loss).
+    /// Range: 0.5 – 4. Default: 2. Applied at next app restart.
+    /// </summary>
+    public double CircuitRetentionHours { get; set; } = DefaultCircuitRetentionHours;
+
+    public int GetSafeIdleTimeoutMinutes()
+    {
+        if (IdleTimeoutMinutes < MinIdleTimeoutMinutes) return MinIdleTimeoutMinutes;
+        if (IdleTimeoutMinutes > MaxIdleTimeoutMinutes) return MaxIdleTimeoutMinutes;
+        return IdleTimeoutMinutes;
+    }
+
+    public double GetSafeCircuitRetentionHours()
+    {
+        if (CircuitRetentionHours < MinCircuitRetentionHours) return MinCircuitRetentionHours;
+        if (CircuitRetentionHours > MaxCircuitRetentionHours) return MaxCircuitRetentionHours;
+        return CircuitRetentionHours;
+    }
+}
+
+/// <summary>
+/// SMTP settings for sending email-based 2FA codes and notifications
+/// </summary>
+public class SmtpSettings
+{
+    public bool IsEnabled { get; set; }
+    public string Host { get; set; } = string.Empty;
+    public int Port { get; set; } = 587;
+    public string Username { get; set; } = string.Empty;
+    public string Password { get; set; } = string.Empty;
+    public string FromEmail { get; set; } = string.Empty;
+    public string FromName { get; set; } = "Reifen Späth Lagerverwaltung";
+    public bool UseSsl { get; set; } = true;
+
+    public bool IsConfigured => !string.IsNullOrWhiteSpace(Host)
+        && !string.IsNullOrWhiteSpace(Username)
+        && !string.IsNullOrWhiteSpace(FromEmail);
+}

Lagerbestand/Models/StorageLocation.cs

@@ -0,0 +1,252 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+using System.Text.RegularExpressions;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a physical storage location in the warehouse.
+/// Storage locations are identified by a 4-digit code in ABCD format:
+/// - A: Gebäude (1=Werkstatt mit 3 Reihen, 2=Lager mit 5 Reihen)
+/// - B: Regalreihe (Werkstatt: 1-3, Lager: 1-5)
+/// - C: Seite/Ebene (1=links oben, 2=links unten, 3=rechts oben, 4=rechts unten)
+/// - D: Platz längs (1-9)
+/// Example: 2235 = Lager, Reihe 2, rechts oben, Platz 5
+/// </summary>
+public class StorageLocation
+{
+    /// <summary>
+    /// Regex pattern for valid location codes: ABCD format
+    /// A = 1-2 (Gebäude), B = 1-5 (Reihe), C = 1-4 (Seite/Ebene), D = 1-9 (Platz)
+    /// </summary>
+    public const string LocationCodePattern = @"^[12][1-5][1-4][1-9]$";
+
+    /// <summary>
+    /// Minimum row number
+    /// </summary>
+    public const int MinRow = 1;
+
+    /// <summary>
+    /// Maximum row number (Lager, Gebäude 2)
+    /// </summary>
+    public const int MaxRow = 5;
+
+    /// <summary>
+    /// Maximum row number for Werkstatt (Gebäude 1)
+    /// </summary>
+    public const int MaxRowWerkstatt = 3;
+
+    /// <summary>
+    /// Maximum row number for Lager (Gebäude 2)
+    /// </summary>
+    public const int MaxRowLager = 5;
+
+    /// <summary>
+    /// Minimum slot number (längs)
+    /// </summary>
+    public const int MinSlot = 1;
+
+    /// <summary>
+    /// Maximum slot number (längs)
+    /// </summary>
+    public const int MaxSlot = 9;
+
+    /// <summary>
+    /// Number of positions per lengthwise slot (links/rechts × oben/unten)
+    /// </summary>
+    public const int PositionsPerSlot = 4;
+
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    /// <summary>
+    /// Unique 4-digit location code in ABCD format (e.g., "2235").
+    /// This is the primary human-readable identifier.
+    /// </summary>
+    [Required]
+    [MaxLength(4)]
+    [RegularExpression(LocationCodePattern, ErrorMessage = "Ungültiges Code-Format. Erwartet: ABCD (z.B. 2235)")]
+    public string Code { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Storage building (Werkstatt=1, Lager=2).
+    /// Corresponds to position A in the location code.
+    /// </summary>
+    [Required]
+    public AreaType Area { get; set; } = AreaType.Lager;
+
+    /// <summary>
+    /// Shelf row number within the building (Werkstatt: 1-3, Lager: 1-5).
+    /// Corresponds to position B in the location code.
+    /// </summary>
+    [Required]
+    [Range(MinRow, MaxRow, ErrorMessage = "Reihe muss zwischen 1 und 5 liegen.")]
+    public int Row { get; set; } = 1;
+
+    /// <summary>
+    /// Position within the shelf slot: side (links/rechts) and level (oben/unten).
+    /// Corresponds to position C in the location code.
+    /// </summary>
+    [Required]
+    public ShelfPosition Position { get; set; } = ShelfPosition.LinksOben;
+
+    /// <summary>
+    /// Lengthwise slot number within the row (1-9).
+    /// Corresponds to position D in the location code.
+    /// </summary>
+    [Required]
+    [Range(MinSlot, MaxSlot, ErrorMessage = "Platz muss zwischen 1 und 9 liegen.")]
+    public int SlotNumber { get; set; } = 1;
+
+    /// <summary>
+    /// Whether this location is currently occupied by a tire stack.
+    /// </summary>
+    public bool IsOccupied { get; set; }
+
+    /// <summary>
+    /// The ID of the tire stack currently stored at this location (if occupied).
+    /// </summary>
+    public Guid? TireStackId { get; set; }
+
+    /// <summary>
+    /// Navigation property to the tire stack at this location.
+    /// </summary>
+    [ForeignKey(nameof(TireStackId))]
+    public TireStack? OccupiedTireStack { get; set; }
+
+    /// <summary>
+    /// When the current tire stack was placed at this location.
+    /// </summary>
+    public DateTime? OccupiedSince { get; set; }
+
+    /// <summary>
+    /// Optional notes about this location.
+    /// </summary>
+    [MaxLength(500)]
+    public string? Notes { get; set; }
+
+    /// <summary>
+    /// Whether this location is available for new storage (not blocked).
+    /// </summary>
+    public bool IsAvailable { get; set; } = true;
+
+    /// <summary>
+    /// Whether this location is active in the system.
+    /// </summary>
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>
+    /// Navigation property for tire stacks stored at this location (legacy support).
+    /// </summary>
+    public ICollection<TireStack> TireStacks { get; set; } = new List<TireStack>();
+
+    /// <summary>
+    /// Display name showing the human-readable location.
+    /// </summary>
+    [NotMapped]
+    public string DisplayName => $"{Area.GetDisplayName()}, Reihe {Row}, {Position.GetDisplayName()}, Platz {SlotNumber}";
+
+    /// <summary>
+    /// Short display for compact views.
+    /// </summary>
+    [NotMapped]
+    public string ShortDisplay => $"{Area.GetDisplayName()} R{Row} {Position.GetShortName()} P{SlotNumber}";
+
+    /// <summary>
+    /// Full path description of the location.
+    /// </summary>
+    [NotMapped]
+    public string FullPath => $"{Area.GetBuildingLabel()} / Reihe {Row} / {Position.GetDisplayName()} / Platz {SlotNumber}";
+
+    /// <summary>
+    /// Current occupancy count (number of stacks stored).
+    /// </summary>
+    [NotMapped]
+    public int CurrentOccupancy => IsOccupied ? 1 : 0;
+
+    /// <summary>
+    /// Capacity is always 1 for the new system (one stack per location).
+    /// </summary>
+    [NotMapped]
+    public int Capacity => 1;
+
+    /// <summary>
+    /// Generates the location code from the component parts.
+    /// </summary>
+    public void GenerateCode()
+    {
+        Code = $"{(int)Area}{Row}{(int)Position}{SlotNumber}";
+    }
+
+    /// <summary>
+    /// Parses the location code and populates the Area, Row, Position, and SlotNumber properties.
+    /// </summary>
+    /// <returns>True if parsing was successful</returns>
+    public bool ParseCode()
+    {
+        if (string.IsNullOrWhiteSpace(Code) || Code.Length != 4)
+            return false;
+
+        if (!Regex.IsMatch(Code, LocationCodePattern))
+            return false;
+
+        if (!AreaTypeExtensions.TryFromCode(Code[0], out var area))
+            return false;
+
+        if (!int.TryParse(Code[1].ToString(), out var row) || row < MinRow || row > area.GetMaxRow())
+            return false;
+
+        if (!ShelfPositionExtensions.TryFromCode(Code[2], out var position))
+            return false;
+
+        if (!int.TryParse(Code[3].ToString(), out var slot) || slot < MinSlot || slot > MaxSlot)
+            return false;
+
+        Area = area;
+        Row = row;
+        Position = position;
+        SlotNumber = slot;
+        return true;
+    }
+
+    /// <summary>
+    /// Validates that the current Code matches the Area, Row, Position, and SlotNumber values.
+    /// </summary>
+    public bool ValidateCodeConsistency()
+    {
+        var expectedCode = $"{(int)Area}{Row}{(int)Position}{SlotNumber}";
+        return Code == expectedCode;
+    }
+
+    /// <summary>
+    /// Assigns a tire stack to this location.
+    /// </summary>
+    /// <param name="tireStackId">The ID of the tire stack to assign</param>
+    /// <exception cref="InvalidOperationException">If location is already occupied</exception>
+    public void AssignTireStack(Guid tireStackId)
+    {
+        if (IsOccupied)
+            throw new InvalidOperationException($"Lagerplatz {Code} ist bereits belegt.");
+
+        TireStackId = tireStackId;
+        IsOccupied = true;
+        OccupiedSince = DateTime.UtcNow;
+        UpdatedAt = DateTime.UtcNow;
+    }
+
+    /// <summary>
+    /// Clears the tire stack from this location.
+    /// </summary>
+    public void ClearLocation()
+    {
+        TireStackId = null;
+        OccupiedTireStack = null;
+        IsOccupied = false;
+        OccupiedSince = null;
+        UpdatedAt = DateTime.UtcNow;
+    }
+}

Lagerbestand/Models/TireItem.cs

@@ -0,0 +1,111 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Tire position in a stack
+/// </summary>
+public enum TirePosition
+{
+    FrontLeft = 0,
+    FrontRight = 1,
+    RearLeft = 2,
+    RearRight = 3
+}
+
+/// <summary>
+/// Tire condition rating
+/// </summary>
+public enum TireCondition
+{
+    Excellent = 0,  // Like new
+    Good = 1,       // Normal wear
+    Fair = 2,       // Noticeable wear but safe
+    Poor = 3,       // Should be replaced soon
+    Critical = 4    // Unsafe, needs replacement
+}
+
+/// <summary>
+/// Represents an individual tire within a tire stack.
+/// Allows detailed tracking of each tire's condition.
+/// A TireStack always has exactly 4 TireItems.
+/// </summary>
+public class TireItem
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    /// <summary>
+    /// The tire stack this item belongs to
+    /// </summary>
+    public Guid TireStackId { get; set; }
+
+    [ForeignKey(nameof(TireStackId))]
+    public TireStack? TireStack { get; set; }
+
+    /// <summary>
+    /// Position of this tire in the stack
+    /// </summary>
+    public TirePosition Position { get; set; }
+
+    /// <summary>
+    /// Individual tread depth for this tire in mm
+    /// </summary>
+    [Range(0, 10)]
+    public decimal? TreadDepth { get; set; }
+
+    /// <summary>
+    /// Condition rating for this tire
+    /// </summary>
+    public TireCondition Condition { get; set; } = TireCondition.Good;
+
+    /// <summary>
+    /// Any damage or issues noted
+    /// </summary>
+    [MaxLength(500)]
+    public string? DamageNotes { get; set; }
+
+    /// <summary>
+    /// Individual DOT code if different from stack
+    /// </summary>
+    [MaxLength(20)]
+    public string? DotCode { get; set; }
+
+    /// <summary>
+    /// Photo filename for tire condition documentation
+    /// </summary>
+    [MaxLength(500)]
+    public string? PhotoFileName { get; set; }
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>
+    /// Position display text in German
+    /// </summary>
+    [NotMapped]
+    public string PositionText => Position switch
+    {
+        TirePosition.FrontLeft => "Vorne Links",
+        TirePosition.FrontRight => "Vorne Rechts",
+        TirePosition.RearLeft => "Hinten Links",
+        TirePosition.RearRight => "Hinten Rechts",
+        _ => "Unbekannt"
+    };
+
+    /// <summary>
+    /// Condition display text in German
+    /// </summary>
+    [NotMapped]
+    public string ConditionText => Condition switch
+    {
+        TireCondition.Excellent => "Sehr gut",
+        TireCondition.Good => "Gut",
+        TireCondition.Fair => "Ausreichend",
+        TireCondition.Poor => "Mangelhaft",
+        TireCondition.Critical => "Kritisch",
+        _ => "Unbekannt"
+    };
+}

Lagerbestand/Models/TireStack.cs

@@ -0,0 +1,259 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Status of a tire stack in the storage system
+/// </summary>
+public enum TireStackStatus
+{
+    /// <summary>
+    /// Tires are currently stored in the warehouse
+    /// </summary>
+    Stored = 0,
+
+    /// <summary>
+    /// Tires have been picked up by the customer
+    /// </summary>
+    PickedUp = 1,
+
+    /// <summary>
+    /// Tires have been disposed/recycled
+    /// </summary>
+    Disposed = 2,
+
+    /// <summary>
+    /// Tires are reserved for pickup
+    /// </summary>
+    Reserved = 3,
+
+    /// <summary>
+    /// Tires are in inventory (shop stock, not customer-owned)
+    /// </summary>
+    Inventory = 4
+}
+
+/// <summary>
+/// Represents a stack of exactly 4 tires as a single indivisible unit.
+/// A stack is always 4 identical tires - there is no variable count.
+/// This is the main entity that tracks customer tire storage and shop inventory.
+/// </summary>
+public class TireStack
+{
+    /// <summary>
+    /// Number of tires in a stack - always 4
+    /// </summary>
+    public const int TiresPerStack = 4;
+
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    /// <summary>
+    /// Custom item count for inventory (default: 4 = standard stack).
+    /// Only used for inventory items. Customer stacks always use TiresPerStack.
+    /// </summary>
+    [Range(1, 99)]
+    public int ItemCount { get; set; } = TiresPerStack;
+
+    /// <summary>
+    /// Unique identifier/ticket number for this tire stack (e.g., "TS-2024-0001")
+    /// This serves as the primary human-readable identifier.
+    /// </summary>
+    [Required]
+    [MaxLength(50)]
+    public string TicketNumber { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Customer who owns these tires (null for shop inventory)
+    /// </summary>
+    public Guid? CustomerId { get; set; }
+
+    [ForeignKey(nameof(CustomerId))]
+    public Customer? Customer { get; set; }
+
+    /// <summary>
+    /// Vehicle these tires belong to (null for shop inventory or legacy data)
+    /// </summary>
+    public Guid? VehicleId { get; set; }
+
+    [ForeignKey(nameof(VehicleId))]
+    public Vehicle? Vehicle { get; set; }
+
+    /// <summary>
+    /// Current storage location (null if picked up)
+    /// </summary>
+    public Guid? StorageLocationId { get; set; }
+
+    [ForeignKey(nameof(StorageLocationId))]
+    public StorageLocation? StorageLocation { get; set; }
+
+    /// <summary>
+    /// Tire category/type (used for inventory categorization)
+    /// </summary>
+    public Guid? CatalogItemId { get; set; }
+
+    [ForeignKey(nameof(CatalogItemId))]
+    public CatalogItem? CatalogItem { get; set; }
+
+    /// <summary>
+    /// Current status of the tire stack
+    /// </summary>
+    public TireStackStatus Status { get; set; } = TireStackStatus.Stored;
+
+    /// <summary>
+    /// Tire size (e.g., "225/45R17")
+    /// </summary>
+    [MaxLength(50)]
+    public string? TireSize { get; set; }
+
+    /// <summary>
+    /// Tire brand (e.g., "Michelin", "Continental")
+    /// </summary>
+    [MaxLength(100)]
+    public string? TireBrand { get; set; }
+
+    /// <summary>
+    /// Tire model (e.g., "Pilot Sport 4", "WinterContact TS 860")
+    /// </summary>
+    [MaxLength(100)]
+    public string? TireModel { get; set; }
+
+    /// <summary>
+    /// Season type
+    /// </summary>
+    public TireSeason Season { get; set; } = TireSeason.Sommer;
+
+    /// <summary>
+    /// Tread depth in mm (average of all 4 tires)
+    /// </summary>
+    [Range(0, 10)]
+    public decimal? TreadDepth { get; set; }
+
+    /// <summary>
+    /// DOT/manufacturing date code (e.g., "2523" = week 25 of 2023)
+    /// </summary>
+    [MaxLength(20)]
+    public string? DotCode { get; set; }
+
+    /// <summary>
+    /// Whether tires are mounted on rims
+    /// </summary>
+    public bool WithRims { get; set; } = true;
+
+    /// <summary>
+    /// Rim size if with rims (e.g., "17 Zoll")
+    /// </summary>
+    [MaxLength(20)]
+    public string? RimSize { get; set; }
+
+    /// <summary>
+    /// TPMS sensors present
+    /// </summary>
+    public bool HasTpms { get; set; }
+
+    /// <summary>
+    /// Tire condition rating
+    /// </summary>
+    public TireCondition Condition { get; set; } = TireCondition.Good;
+
+    /// <summary>
+    /// Additional notes about the tire condition or special requirements
+    /// </summary>
+    [MaxLength(1000)]
+    public string? Notes { get; set; }
+
+    /// <summary>
+    /// Date when tires were stored
+    /// </summary>
+    public DateTime StoredAt { get; set; } = DateTime.UtcNow;
+
+    /// <summary>
+    /// Date when tires were picked up
+    /// </summary>
+    public DateTime? PickedUpAt { get; set; }
+
+    /// <summary>
+    /// Expected pickup date (next season change)
+    /// </summary>
+    public DateTime? ExpectedPickupDate { get; set; }
+
+    /// <summary>
+    /// User who stored the tires
+    /// </summary>
+    public Guid? StoredByUserId { get; set; }
+
+    /// <summary>
+    /// User who processed the pickup
+    /// </summary>
+    public Guid? PickedUpByUserId { get; set; }
+
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>
+    /// Whether this is shop inventory (not customer-owned)
+    /// </summary>
+    [NotMapped]
+    public bool IsInventory => CustomerId == null;
+
+    /// <summary>
+    /// Display name - customer name or category name for inventory
+    /// </summary>
+    [NotMapped]
+    public string DisplayName => Customer?.FullName ?? CatalogItem?.Name ?? "Lagerbestand";
+
+    /// <summary>
+    /// Summary description for display
+    /// </summary>
+    [NotMapped]
+    public string Summary
+    {
+        get
+        {
+            var parts = new List<string>();
+            if (!string.IsNullOrEmpty(TireBrand)) parts.Add(TireBrand);
+            if (!string.IsNullOrEmpty(TireSize)) parts.Add(TireSize);
+            parts.Add(Season.ToString());
+            if (WithRims) parts.Add("mit Felgen");
+            return string.Join(" | ", parts);
+        }
+    }
+
+    /// <summary>
+    /// Status display text in German
+    /// </summary>
+    [NotMapped]
+    public string StatusText => Status switch
+    {
+        TireStackStatus.Stored => "Eingelagert",
+        TireStackStatus.PickedUp => "Abgeholt",
+        TireStackStatus.Disposed => "Entsorgt",
+        TireStackStatus.Reserved => "Reserviert",
+        TireStackStatus.Inventory => "Lagerbestand",
+        _ => "Unbekannt"
+    };
+
+    /// <summary>
+    /// Days stored (for billing purposes)
+    /// </summary>
+    [NotMapped]
+    public int DaysStored => (PickedUpAt ?? DateTime.UtcNow).Subtract(StoredAt).Days;
+
+    /// <summary>
+    /// Condition display text in German
+    /// </summary>
+    [NotMapped]
+    public string ConditionText => Condition switch
+    {
+        TireCondition.Excellent => "Sehr gut",
+        TireCondition.Good => "Gut",
+        TireCondition.Fair => "Ausreichend",
+        TireCondition.Poor => "Mangelhaft",
+        TireCondition.Critical => "Kritisch",
+        _ => "Unbekannt"
+    };
+}

Lagerbestand/Models/Vehicle.cs

@@ -0,0 +1,92 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Lagerbestand.Models;
+
+/// <summary>
+/// Represents a vehicle owned by a customer.
+/// A customer can have multiple vehicles, each with their own tire stacks.
+/// </summary>
+public class Vehicle
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    /// <summary>
+    /// The customer who owns this vehicle
+    /// </summary>
+    public Guid CustomerId { get; set; }
+
+    [ForeignKey(nameof(CustomerId))]
+    public Customer? Customer { get; set; }
+
+    /// <summary>
+    /// Vehicle manufacturer (e.g., "BMW", "Mercedes", "VW")
+    /// </summary>
+    [Required]
+    [MaxLength(100)]
+    public string Make { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Vehicle model (e.g., "3er", "C-Klasse", "Golf")
+    /// </summary>
+    [MaxLength(100)]
+    public string? Model { get; set; }
+
+    /// <summary>
+    /// Tire size for this vehicle (e.g., "225/45 R17")
+    /// </summary>
+    [Required]
+    [MaxLength(50)]
+    public string TireSize { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Additional notes about the vehicle
+    /// </summary>
+    [MaxLength(500)]
+    public string? Notes { get; set; }
+
+    /// <summary>
+    /// Whether this is the customer's primary/default vehicle
+    /// </summary>
+    public bool IsPrimary { get; set; }
+
+    /// <summary>
+    /// Whether the vehicle is active (not deleted)
+    /// </summary>
+    public bool IsActive { get; set; } = true;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? UpdatedAt { get; set; }
+
+    /// <summary>
+    /// Navigation property for tire stacks stored for this vehicle
+    /// </summary>
+    public ICollection<TireStack> TireStacks { get; set; } = new List<TireStack>();
+
+    /// <summary>
+    /// Display name combining make, model, and tire size
+    /// </summary>
+    [NotMapped]
+    public string DisplayName
+    {
+        get
+        {
+            var name = Make;
+            if (!string.IsNullOrEmpty(Model))
+                name += $" {Model}";
+            if (!string.IsNullOrEmpty(TireSize))
+                name += $" ({TireSize})";
+            return name;
+        }
+    }
+
+    /// <summary>
+    /// Short display showing just make (for compact views)
+    /// </summary>
+    [NotMapped]
+    public string ShortName => !string.IsNullOrEmpty(Model)
+        ? $"{Make} {Model}"
+        : Make;
+}