Refactor CRUD module imports and usage for clarity.

Replaces ambiguous shorthand references like `event` and `user` with more descriptive names such as `event_crud` and `user_crud`. Updates imports, function calls, tests, and other references across the codebase to maintain consistency. This improves code readability and reduces potential confusion.

backend/app/services/auth_service.py

@@ -15,7 +15,7 @@ from app.core.auth import (
 )
 from app.models.user import User
 from app.schemas.users import Token, UserCreate
-from app.crud.user import user as crud_user
+from app.crud.user import user_crud as crud_user
 from app.core.auth import decode_token, get_token_data
 
 logger = logging.getLogger(__name__)