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/EmailTemplates/Commands/Update/UpdateEmailTemplateCommandHandler.cs

@@ -22,6 +22,7 @@ public class UpdateEmailTemplateCommandHandler : IRequestHandler<UpdateEmailTemp
     /// 
     /// </summary>
     /// <param name="repository"></param>
+    /// <param name="mapper"></param>
     public UpdateEmailTemplateCommandHandler(IRepository<EmailTemplate> repository, IMapper mapper)
     {
         _repository = repository;