- Update GET /v3/data_store/code/{code} to support 'limit' query parameter.
- Refactor return logic: returns single object if limit=1, otherwise returns a list.
- Clean up formatting in GUIDE__V3_FRONTEND_API.md and sync to agents_sync.
- Finalize unified E2E test script: tests/e2e/test_e2e_v3_data_store_lookup.py.