Add audit logging, processing stages, delete functionality, and bug fixes

- Add audit logging system for tracking CV uploads, processing, deletion,
  report views, and PDF exports for billing/reference purposes
- Add processing stage display on dashboard instead of generic "Processing"
- Add delete button for CV checks on dashboard
- Fix duplicate primary key error in CompanyCache (race condition)
- Fix DbContext concurrency in Dashboard (concurrent delete/load operations)
- Fix ProcessCVCheckJob to handle deleted records gracefully
- Fix duplicate flags in verification report by deduplicating on Title+Description
- Remove internal cache notes from verification results
- Add EF migrations for ProcessingStage and AuditLog table

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/TrueCV.Application/DTOs/CVCheckDto.cs

@@ -6,6 +6,7 @@ public sealed record CVCheckDto
     public required string OriginalFileName { get; init; }
     public required string Status { get; init; }
     public int? VeracityScore { get; init; }
+    public string? ProcessingStage { get; init; }
     public required DateTime CreatedAt { get; init; }
     public DateTime? CompletedAt { get; init; }
 }