Three-stage Dockerfile: frontend-build (Node 20), api (Python 3.12 + uvicorn),
web (nginx 1.27). nginx.conf proxies /api and /ws to the API service with
WebSocket upgrade support. Includes backend/requirements.txt with all Python
deps, frontend scaffolding (Vite + React + TypeScript + Tailwind), and
placeholder alembic files for Docker COPY compatibility.