Refactor EnvelopeReceiverPage for modular data handling

Refactored `EnvelopeReceiverPage.razor` to use new services for receiver authentication and data retrieval. Introduced `EnvelopeReceiverAuthorizationService` for handling JWT-based authorization and `EnvelopeReceiverPageDataService` for centralized data access and caching. Updated dependency injection in `Program.cs` to register these services.

Replaced direct service calls with `PageDataService` methods for document, signature, and receiver data retrieval. Improved logging with `ILogger` and added debug logs for token validation. Enhanced modularity, maintainability, and performance by consolidating logic and reducing coupling between components.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs

@@ -331,6 +331,8 @@ try
 
     // SSR Authentication Service (for Envelope Receiver pages)
     builder.Services.AddScoped<EnvelopeGenerator.Server.Services.IEnvelopeAuthService, EnvelopeGenerator.Server.Services.EnvelopeAuthService>();
+    builder.Services.AddScoped<EnvelopeGenerator.Server.Services.EnvelopeReceiverAuthorizationService>();
+    builder.Services.AddScoped<EnvelopeGenerator.Server.Services.EnvelopeReceiverPageDataService>();
 
     // DevExpress Server-Side Services (CRITICAL for DxPdfViewer)
     builder.Services.AddDevExpressBlazor();