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/api/routes/event_themes.py

@@ -9,7 +9,7 @@ from sqlalchemy.orm import Session
 from app.api.dependencies.common import get_storage_provider
 from app.api.dependencies.auth import get_current_user
 from app.core.database import get_db
-from app.crud.event_theme import event_theme as event_theme_crud
+from app.crud.event_theme import event_theme_crud as event_theme_crud
 from app.models import User
 from app.schemas.event_themes import EventThemeCreate, EventThemeResponse, EventThemeUpdate
 from app.core.storage import StorageProvider