Refactor(backend): improve formatting in services, repositories & tests

- Consistently format multi-line function headers, exception handling, and repository method calls for readability.
- Reorganize misplaced imports across modules (e.g., services & tests) into proper sorted order.
- Adjust indentation, line breaks, and spacing inconsistencies in tests and migration files.
- Cleanup unnecessary trailing newlines and reorganize `__all__` declarations for consistency.

backend/tests/repositories/test_session.py

@@ -9,8 +9,8 @@ from uuid import uuid4
 import pytest
 
 from app.core.repository_exceptions import InvalidInputError
-from app.repositories.session import session_repo as session_crud
 from app.models.user_session import UserSession
+from app.repositories.session import session_repo as session_crud
 from app.schemas.sessions import SessionCreate