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/SignatureController.cs

@@ -38,9 +38,9 @@ public class SignatureController : ControllerBase
     [HttpGet("{envelopeKey}")]
     public async Task<IActionResult> GetAnnotsOfReceiver(string envelopeKey, CancellationToken cancel)
     {
-        int envelopeId = User.GetEnvelopeIdOfReceiver();
+        int envelopeId = User.EnvelopeId();
 
-        int receiverId = User.GetReceiverIdOfReceiver();
+        int receiverId = User.ReceiverId();
 
         var doc = await _mediator.Send(new ReadDocumentQuery() { EnvelopeId = envelopeId }, cancel);