Add TODOs for middleware, generic service, and CQRS

Added TODO comments in Program.cs for exception handling middleware, and in CatalogService.cs and ICatalogService.cs for creating a generic service and implementing CQRS with MediatR. No functional changes made.

DbFirst.Application/Catalogs/CatalogService.cs

@@ -4,6 +4,8 @@ using DbFirst.Domain.Entities;
 
 namespace DbFirst.Application.Catalogs;
 
+//TODO: create generic service to reduce code duplication
+//TODO: implement CQRS pattern with MediatR
 public class CatalogService : ICatalogService
 {
     private readonly ICatalogRepository _repository;