Refactor claim handling and simplify controllers

Refactored multiple controllers (`AnnotationController`,
`DocumentController`, `ReadOnlyController`, and
`SignatureController`) to use updated claim extension methods
(`ReceiverSignature`, `EnvelopeUuid`, etc.), replacing older,
verbose methods for improved readability and consistency.

Removed the `EnvelopeClaimTypes` class and replaced claim type
constants with `EnvelopeClaimNames`. Simplified claim retrieval
logic in `ReceiverClaimExtensions` by consolidating methods and
removing redundant or unused functionality.

Eliminated the `SignInEnvelopeAsync` method, indicating a shift
away from manual claim management. Performed general cleanup,
including removing obsolete code and improving exception
messages for better debugging context.

EnvelopeGenerator.API/Controllers/DocumentController.cs

@@ -51,7 +51,7 @@ public class DocumentController(IMediator mediator, IAuthorizationService authSe
             if (query is not null)
                 return BadRequest("Query parameters are not allowed for receiver role.");
 
-            var envelopeId = User.GetEnvelopeIdOfReceiver();
+            var envelopeId = User.EnvelopeId();
             var receiverDoc = await mediator.Send(new ReadDocumentQuery { EnvelopeId = envelopeId }, cancel);
             return receiverDoc.ByteData is byte[] receiverDocByte
                 ? File(receiverDocByte, "application/octet-stream")
@@ -71,7 +71,7 @@ public class DocumentController(IMediator mediator, IAuthorizationService authSe
     [HttpGet("{envelopeKey}")]
     public async Task<IActionResult> GetDocumentOfReceiver(string envelopeKey, CancellationToken cancel)
     {
-        int envelopeId = User.GetEnvelopeIdOfReceiver();
+        int envelopeId = User.EnvelopeId();
 
         var senderDoc = await mediator.Send(new ReadDocumentQuery() { EnvelopeId = envelopeId }, cancel);