Server side:
- service-coordinator-ws: full WS implementation using ws package
- Auth via ?token=<kiosk_key> query param
- Coordinator registry for cross-plugin notification
- Admin mutations call notifyKiosks() → server pushes reload-bundle
- 30s ping/pong heartbeat
Kiosk side:
- Rust ws_client with tokio runtime + tokio-tungstenite
- Auto-reconnect with exponential backoff (1s → 60s cap)
- On reload-bundle: re-fetches bundle, re-renders layout
- Pong replies to server pings
Also fix: auto-suffix kiosk name on UNIQUE collision (re-pair with
same hostname no longer fails).
