Refactor DTOs and tests; add framework-specific handling

Refactored the codebase to use shared DTOs from `DocumentService.Application.Common.DTOs`, removing inline DTO definitions in client interfaces and tests. Introduced conditional compilation to handle framework-specific differences in DTOs and handlers.

Updated test cases to align with the new DTO structures, including `SwissQrCodeExtractionResult`, `PdfValidationResult`, and `ZugferdExtractionResult`. Adjusted test data to match updated DTO properties.

Cleaned up solution and project files, ensuring proper references and organization. Removed unused files and fixed project references in `DocumentService.Tests.csproj`. Improved maintainability and consistency across the codebase.

DocumentService.Application/ExtractZugferd/ExtractZugferdCommand.cs

@@ -18,6 +18,7 @@ public record ExtractZugferdCommand : IRequest<ZugferdExtractionResult>
     public required Stream PdfStream { get; init; }
 }
 
+#if NET
 /// <summary>
 /// Handler for ExtractZugferdCommand.
 /// Extracts ZUGFeRD XML from PDF and returns XML content
@@ -77,6 +78,7 @@ public class ExtractZugferdCommandHandler(
         };
     }
 }
+#endif
 
 /// <summary>
 /// Validator for ExtractZugferdCommand.