feat(api): fast FastAPI app + model loader refactor; add mock mode for tests\n\n- Add pyproject + setuptools config and console entrypoint\n- Implement enhanced field extraction + MRZ heuristics\n- Add response builder with compatibility for legacy MRZ fields\n- New preprocessing pipeline for PDFs/images\n- HF Spaces GPU: cache ENV, optional flash-attn, configurable base image\n- Add Make targets for Spaces GPU and local CPU\n- Add httpx for TestClient; tests pass in mock mode\n- Remove embedded model files and legacy app/modules
