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/crud/event.py

@@ -170,4 +170,4 @@ class CRUDEvent(CRUDBase[Event, EventCreate, EventUpdate]):
 
 
 # Create a singleton instance for use across the application
-event = CRUDEvent(Event)
+event_crud = CRUDEvent(Event)

backend/app/crud/event_theme.py

@@ -22,4 +22,4 @@ class CRUDEventTheme(CRUDBase[EventTheme, EventThemeCreate, EventThemeUpdate]):
         )
 
 
-event_theme = CRUDEventTheme(EventTheme)
+event_theme_crud = CRUDEventTheme(EventTheme)

backend/app/crud/user.py

@@ -53,4 +53,4 @@ class CRUDUser(CRUDBase[User, UserCreate, UserUpdate]):
 
 
 # Create a singleton instance for use across the application
-user = CRUDUser(User)
+user_crud = CRUDUser(User)