Replace UUID with DocumentElementId across the codebase

Updated `PdfSignOptionsDto` and `PdfSignatureCheckItemDto` to use `DocumentElementId` (long) instead of `UUID` (string). Modified `PdfDigitalSignatureService` to reflect this change, including updates to `SignatureReasonMetaRegex`, `BuildReasonWithMeta`, and `ParseReasonMeta`. Adjusted method signatures, return values, and property assignments to ensure consistent use of `DocumentElementId`. These changes align with a shift in the application's data model to use numeric identifiers for document elements.

EnvelopeGenerator.Application/Common/Dto/PdfSignOptionsDto.cs

@@ -10,7 +10,7 @@ public sealed record PdfSignOptionsDto
     /// <summary>
     /// 
     /// </summary>
-    public string UUID { get; set; } = null!;
+    public long DocumentElementId { get; set; }
 
     /// <summary>
     /// 

EnvelopeGenerator.Application/Common/Dto/PdfSignatureCheckResultDto.cs

@@ -47,7 +47,7 @@ public sealed record PdfSignatureCheckItemDto(
     string? Filter,
     string? SubFilter,
     string? ApplicationName,
-    string? UUID,
+    long? DocumentElementId,
     string? OriginalDocumentSha256,
     string? MessageDigestHex,
     string? Error);