test(backend): add comprehensive tests for OAuth and agent endpoints

- Added tests for OAuth provider admin and consent endpoints covering edge cases.
- Extended agent-related tests to handle incorrect project associations and lifecycle state transitions.
- Introduced tests for sprint status transitions and validation checks.
- Improved multiline formatting consistency across all test functions.

backend/tests/crud/test_base.py

@@ -12,7 +12,7 @@ from sqlalchemy.exc import DataError, IntegrityError, OperationalError
 from sqlalchemy.orm import joinedload
 
 from app.crud.user import user as user_crud
-from app.schemas.users import UserCreate, UserUpdate
+from app.schemas.users import UserCreate
 
 
 class TestCRUDBaseGet: