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/Receivers/Commands/CreateReceiverCommand.cs

@@ -67,6 +67,7 @@ public class CreateReceiverCommandHandler : IRequestHandler<CreateReceiverComman
     /// 
     /// </summary>
     /// <param name="repo"></param>
+    /// <param name="mapper"></param>
     public CreateReceiverCommandHandler(IRepository<Receiver> repo, IMapper mapper)
     {
         _repo = repo;
@@ -81,7 +82,7 @@ public class CreateReceiverCommandHandler : IRequestHandler<CreateReceiverComman
     /// <returns></returns>
     public async Task<(ReceiverDto Receiver, bool AlreadyExists)> Handle(CreateReceiverCommand request, CancellationToken cancel)
     {
-        var receiver = await _repo.ReadOnly()
+        var receiver = await _repo.Query
             .Where(r => r.EmailAddress == request.EmailAddress)
             .SingleOrDefaultAsync(cancel);