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_db_failures.py

@@ -11,8 +11,8 @@ import pytest
 from sqlalchemy.exc import OperationalError
 
 from app.core.repository_exceptions import IntegrityConstraintError
-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
 
 
@@ -103,7 +103,9 @@ class TestSessionCRUDCreateSessionFailures:
                         last_used_at=datetime.now(UTC),
                     )
 
-                    with pytest.raises(IntegrityConstraintError, match="Failed to create session"):
+                    with pytest.raises(
+                        IntegrityConstraintError, match="Failed to create session"
+                    ):
                         await session_crud.create_session(session, obj_in=session_data)
 
                     mock_rollback.assert_called_once()
@@ -134,7 +136,9 @@ class TestSessionCRUDCreateSessionFailures:
                         last_used_at=datetime.now(UTC),
                     )
 
-                    with pytest.raises(IntegrityConstraintError, match="Failed to create session"):
+                    with pytest.raises(
+                        IntegrityConstraintError, match="Failed to create session"
+                    ):
                         await session_crud.create_session(session, obj_in=session_data)
 
                     mock_rollback.assert_called_once()