refactor: remove PdfMetadata/PdfAMetadata, use result DTOs directly

PdfMetadata and PdfAMetadata were redundant intermediate classes that
mirrored PdfValidationResult and PdfAValidationResult exactly.

Changes:
- Delete PdfMetadata.cs and PdfAMetadata.cs
- IPdfProcessor.ValidateAsync now returns PdfValidationResult directly
- IPdfProcessor.ValidatePdfAAsync now returns PdfAValidationResult directly
- ValidatePdfQueryHandler: remove IMapper dependency, return result directly
- ValidatePdfAQueryHandler: remove IMapper dependency, return result directly
- MappingProfile: remove the two now-obsolete CreateMap calls
- PdfValidationResult: add IsEncrypted parameter (was missing)

DocumentOperator.Application/Common/DTOs/PdfValidationResult.cs

@@ -9,10 +9,12 @@ namespace DocumentService.Application.Common.DTOs;
 /// <param name="PdfVersion">PDF-Version (z.B. "1.4")</param>
 /// <param name="HasAttachments">Hat das PDF Anhänge?</param>
 /// <param name="AttachmentCount">Anzahl der Anhänge</param>
+/// <param name="IsEncrypted">Ist das PDF passwortgeschützt/verschlüsselt?</param>
 public record PdfValidationResult(
     int PageCount,
     long FileSizeBytes,
     double FileSizeMB,
     string PdfVersion,
     bool HasAttachments,
-    int AttachmentCount);
+    int AttachmentCount,
+    bool IsEncrypted);