Add XML docs and standardize repository access patterns

Added XML documentation to extension and handler classes for improved maintainability. Refactored repository access to use .Query instead of .ReadOnly() for consistency. Updated async extension methods for better readability and error handling.

EnvelopeGenerator.Application/EnvelopeReceivers/Queries/ReceiverAlreadySignedQuery.cs

@@ -68,6 +68,6 @@ public class ReceiverAlreadySignedQueryHandler : IRequestHandler<ReceiverAlready
     /// <returns></returns>
     public async Task<bool> Handle(ReceiverAlreadySignedQuery request, CancellationToken cancel = default)
     {
-        return await _repo.ReadOnly().Where(request).Where(h => h.Status == EnvelopeStatus.DocumentSigned).AnyAsync(cancel);
+        return await _repo.Query.Where(request).Where(h => h.Status == EnvelopeStatus.DocumentSigned).AnyAsync(cancel);
     }
 }