feat: L1 server with persistent run storage

- FastAPI server on port 8100
- POST /runs to start rendering jobs
- GET /runs/{id} to check status
- Cache and run persistence in Redis
- Auto-generated API docs at /docs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

requirements.txt

@@ -1,5 +1,7 @@
 celery[redis]>=5.3.0
 redis>=5.0.0
 requests>=2.31.0
+fastapi>=0.109.0
+uvicorn>=0.27.0
 # Core artdag from GitHub
 git+https://github.com/gilesbradshaw/art-dag.git