Phase 18: Database preview/import, version upgrade path, and compatibility matrix

- Add DatabasePreviewService with full import pipeline (table mapping, GUID normalization, FK ordering)
- Add DatabasePreview.razor UI with preview table, conflict detection, and import confirmation
- Update DatabaseSettings.razor with import trigger and status feedback
- Fix GUID case mismatch bug: normalize all GUIDs to uppercase before raw SQL writes
- Add version-upgrade copy block to Program.cs: copies PreviousDbFileName → new DbFileName on first launch after version bump so EF migrations apply against real data instead of blank DB
- Update Compatibility-Matrix.md with versioning policy and DB filename conventions
- Minor: LeaseNotificationService null guard, LeaseWorkflowService status transition fix, Index.razor property count tweak

Author: CIS Guru

2-Nine.Application/Models/DTOs/DatabasePreviewDTOs.cs

@@ -10,10 +10,17 @@ public class DatabasePreviewData
     public int LeaseCount { get; set; }
     public int InvoiceCount { get; set; }
     public int PaymentCount { get; set; }
-    
+    public int MaintenanceCount { get; set; }
+    public int RepairCount { get; set; }
+    public int DocumentCount { get; set; }
+
     public List<PropertyPreview> Properties { get; set; } = new();
     public List<TenantPreview> Tenants { get; set; } = new();
     public List<LeasePreview> Leases { get; set; } = new();
+    public List<InvoicePreview> Invoices { get; set; } = new();
+    public List<PaymentPreview> Payments { get; set; } = new();
+    public List<MaintenancePreview> MaintenanceRequests { get; set; } = new();
+    public List<RepairPreview> Repairs { get; set; } = new();
 }
 
 /// <summary>
@@ -60,17 +67,111 @@ public class LeasePreview
     public string Status { get; set; } = string.Empty;
 }
 
+/// <summary>
+/// DTO for invoice preview in read-only database view
+/// </summary>
+public class InvoicePreview
+{
+    public Guid Id { get; set; }
+    public string InvoiceNumber { get; set; } = string.Empty;
+    public string PropertyAddress { get; set; } = string.Empty;
+    public string TenantName { get; set; } = string.Empty;
+    public DateTime DueOn { get; set; }
+    public decimal Amount { get; set; }
+    public string Status { get; set; } = string.Empty;
+}
+
+/// <summary>
+/// DTO for payment preview in read-only database view
+/// </summary>
+public class PaymentPreview
+{
+    public Guid Id { get; set; }
+    public string PaymentNumber { get; set; } = string.Empty;
+    public string InvoiceNumber { get; set; } = string.Empty;
+    public DateTime PaidOn { get; set; }
+    public decimal Amount { get; set; }
+    public string PaymentMethod { get; set; } = string.Empty;
+}
+
+/// <summary>
+/// DTO for maintenance request preview in read-only database view
+/// </summary>
+public class MaintenancePreview
+{
+    public Guid Id { get; set; }
+    public string Title { get; set; } = string.Empty;
+    public string PropertyAddress { get; set; } = string.Empty;
+    public string RequestType { get; set; } = string.Empty;
+    public string Priority { get; set; } = string.Empty;
+    public string Status { get; set; } = string.Empty;
+    public DateTime RequestedOn { get; set; }
+}
+
+/// <summary>
+/// DTO for repair preview in read-only database view
+/// </summary>
+public class RepairPreview
+{
+    public Guid Id { get; set; }
+    public string PropertyAddress { get; set; } = string.Empty;
+    public string Description { get; set; } = string.Empty;
+    public string RepairType { get; set; } = string.Empty;
+    public DateTime? CompletedOn { get; set; }
+    public decimal Cost { get; set; }
+}
+
+/// <summary>
+/// Represents a non-backup database file found in the data directory (e.g. an older versioned DB)
+/// </summary>
+public class OtherDatabaseFile
+{
+    public string FileName { get; set; } = string.Empty;
+    public string FilePath { get; set; } = string.Empty;
+    public long FileSizeBytes { get; set; }
+    public string FileSizeFormatted => FormatBytes(FileSizeBytes);
+    public DateTime LastModified { get; set; }
+
+    private static string FormatBytes(long bytes)
+    {
+        if (bytes < 1024) return $"{bytes} B";
+        if (bytes < 1_048_576) return $"{bytes / 1024.0:F1} KB";
+        return $"{bytes / 1_048_576.0:F1} MB";
+    }
+}
+
+/// <summary>
+/// Result of a data import operation from a preview database
+/// </summary>
+public class ImportResult
+{
+    public bool Success { get; set; }
+    public string Message { get; set; } = string.Empty;
+    public int PropertiesImported { get; set; }
+    public int TenantsImported { get; set; }
+    public int LeasesImported { get; set; }
+    public int InvoicesImported { get; set; }
+    public int PaymentsImported { get; set; }
+    public int MaintenanceRequestsImported { get; set; }
+    public int RepairsImported { get; set; }
+    public int DocumentsImported { get; set; }
+    public List<string> Errors { get; set; } = new();
+
+    public int TotalImported => PropertiesImported + TenantsImported + LeasesImported
+        + InvoicesImported + PaymentsImported + MaintenanceRequestsImported + RepairsImported + DocumentsImported;
+}
+
 /// <summary>
 /// Result object for database operations
 /// </summary>
 public class DatabaseOperationResult
 {
     public bool Success { get; set; }
     public string Message { get; set; } = string.Empty;
-    
+
     public static DatabaseOperationResult SuccessResult(string message = "Operation successful")
         => new() { Success = true, Message = message };
-    
+
     public static DatabaseOperationResult FailureResult(string message)
         => new() { Success = false, Message = message };
 }