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/init_db.py

@@ -3,7 +3,7 @@ import logging
 from typing import Optional
 from sqlalchemy.orm import Session
 from app.core.config import settings
-from app.crud.user import user as user_crud
+from app.crud.user import user_crud as user_crud
 from app.schemas.users import UserCreate
 from app.core.database import engine
 logger = logging.getLogger(__name__)