refactor(tests): replace crud references with repo across repository test files

- Updated import statements and test logic to align with `repositories` naming changes.
- Adjusted documentation and test names for consistency with the updated naming convention.
- Improved test descriptions to reflect the repository-based structure.

backend/tests/services/test_session_cleanup.py

@@ -206,13 +206,13 @@ class TestCleanupExpiredSessions:
         """Test cleanup returns 0 on database errors (doesn't crash)."""
         _test_engine, AsyncTestingSessionLocal = async_test_db
 
-        # Mock session_crud.cleanup_expired to raise error
+        # Mock session_repo.cleanup_expired to raise error
         with patch(
             "app.services.session_cleanup.SessionLocal",
             return_value=AsyncTestingSessionLocal(),
         ):
             with patch(
-                "app.services.session_cleanup.session_crud.cleanup_expired"
+                "app.services.session_cleanup.session_repo.cleanup_expired"
             ) as mock_cleanup:
                 mock_cleanup.side_effect = Exception("Database connection lost")