Removed unused and redundant using/import statements from multiple files, including command, repository, and Program.cs. No functional changes; this commit improves code clarity and organization.
Replaced direct service usage in CatalogsController with MediatR-based commands and queries for all CRUD operations. Added command/query and handler classes for Catalog operations. Updated dependency injection to register MediatR and removed ICatalogService. Improved code maintainability and testability by adopting CQRS architecture.