Implements packages/backend/src/index.ts:
- Creates WebSocket server on port 18790 (configurable via WS_PORT)
- Instantiates OpenClawBridge and connects to OpenClaw GW
- Transforms bridge agentStateChanged events into frontend-compatible state.diff messages (agent.activity / agent.position ops)
- Sends state.full snapshot on new client connection
- Broadcasts heartbeat pings every 15 seconds
- Handles graceful shutdown on SIGINT/SIGTERM
