Bundle FastAPI backend into Next.js Docker container

The Next.js app was proxying /api/* to the old Flask/FastAPI server
at legal-ai.nautilus.marcusgroup.org. When that server went down,
the Next.js app's API calls failed with 503.

Now both services run in the same container:
- FastAPI (uvicorn) on :8000 — the API backend
- Next.js (node) on :3000 — proxies /api/* to localhost:8000

Changes:
- Dockerfile: multi-stage build with Python 3.12 + Node.js
- next.config.ts: default proxy target is now 127.0.0.1:8000
- start.sh: launches uvicorn in background + node in foreground
- pyproject.toml: add fastapi + uvicorn as explicit deps

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.dockerignore

@@ -4,3 +4,12 @@ mcp-server/.venv/
 **/__pycache__/
 *.pyc
 .git/
+.taskmaster/
+web/static/
+web/__pycache__/
+scripts/
+skills/
+docs/
+legacy/
+node_modules/
+.next/