Add UUID and metadata support for PDF signing

Enhanced PDF signing with UUID and metadata handling:
- Added `UUID` and `OriginalDocumentSha256` to `PdfSignOptionsDto` and `PdfSignatureCheckItemDto`.
- Introduced `BusinessReason` to separate metadata from signature reasons.
- Updated `PdfDigitalSignatureService` to embed and parse metadata in signature reasons.
- Improved error handling to include metadata in validation results.
- Updated `PdfSignatureController` to handle `UUID` in signing requests.

Refactored PKCS#11 configuration:
- Replaced `LibraryPath` with `AssetsRootPath` for asset resolution.
- Added `ProxySocket` and `DefaultApplicationName` options.
- Clarified runtime behavior for asset resolution in `README.md`.

Updated documentation and examples to reflect these changes.

EnvelopeGenerator.Application/Common/Dto/PdfSignOptionsDto.cs

@@ -4,6 +4,7 @@ namespace EnvelopeGenerator.Application.Common.Dto;
 
 public sealed record PdfSignOptionsDto
 {
+    public string? UUID { get; set; }
     public string? Name { get; set; }
     public string? Reason { get; set; }
     public string? Location { get; set; }