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/api/test_auth_security.py

@@ -12,8 +12,8 @@ These tests prevent real-world attack scenarios.
 import pytest
 from httpx import AsyncClient
 
-from app.repositories.session import session_repo as session_crud
 from app.models.user import User
+from app.repositories.session import session_repo as session_crud
 
 
 class TestRevokedSessionSecurity: