Refactor contact info handling in PDF signing

Replaced the `ContactInfo` property with separate `Email` and `Phone` fields in `PdfSignOptionsDto` and `PdfSignatureCheckItemDto` for better granularity. Updated the `PdfDigitalSignatureService` to handle the new fields, introducing `BuildContactInfo` and `ParseContactInfo` methods for constructing and parsing contact information.

Modified the `PdfSignatureController` to reflect these changes, updating request models and the `SignPdfAsync` method. Updated the `README.md` to document the new structure. These changes improve the clarity and structure of contact information handling.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Controllers/PdfSignatureController.cs

@@ -17,7 +17,8 @@ public class PdfSignatureController(IPdfDigitalSignatureService signatureService
         public string? Name { get; set; }
         public string? Reason { get; set; }
         public string? Location { get; set; }
-        public string? ContactInfo { get; set; }
+        public string? Email { get; set; }
+        public string? Phone { get; set; }
     }
 
     public sealed class CheckPdfSignatureForm
@@ -52,7 +53,8 @@ public class PdfSignatureController(IPdfDigitalSignatureService signatureService
             Name = request.Name,
             Reason = request.Reason,
             Location = request.Location,
-            ContactInfo = request.ContactInfo,
+            Email = request.Email,
+            Phone = request.Phone,
             CertificationLevel = PdfSignatureCertificationLevel.FormFillingAndAnnotations
         };