- Create lightsync/api/audio.py with POST /load and GET /state endpoints
- Validate file existence and extension (.mp3/.wav/.flac/.ogg)
- Use asyncio.to_thread for engine.load to avoid blocking event loop
- Return 404/400/503 on error conditions
- Register audio router at /api/audio prefix in main.py
- AUD-02 (YouTube) noted as Phase 6 deferral
- Add broadcast_loop sending position ticks at 10Hz to all clients
- Replace echo stub with play/pause/seek/load command dispatch to MPVEngine
- Start broadcast_loop as asyncio task in lifespan, cancel on shutdown
- Use get_engine callable to avoid circular import at module level
- DeviceRegistry with load/save/add/remove/instantiate and _DEVICE_CLASSES dict
- ShowStore with save/load/list_ids using aiofiles for async I/O
- FastAPI app with lifespan hook (startup: load registry/store, shutdown: save registry)
- API routes: GET/POST /api/devices/, DELETE /api/devices/{id}, GET/POST /api/shows/, GET /api/shows/{id}
- WebSocket stub at /ws with ConnectionManager and ack echo
- Frontend shell: DAW layout with header, sidebar (DEVICES + ANIMATIONS), TIMELINE, TRANSPORT
- Terminal aesthetic: dark theme, cyan accents, monospace fonts, no drop shadows
- .gitignore for runtime data (devices.json, shows/, __pycache__, .venv)
