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/tests/crud/test_event.py

@@ -3,7 +3,7 @@ from datetime import datetime, timedelta, timezone
 from uuid import UUID, uuid4
 from zoneinfo import ZoneInfo
 
-from app.crud.event import event as crud_event
+from app.crud.event import event_crud as crud_event
 from app.schemas.events import EventCreate, EventUpdate
 from app.models.event import Event