feat(api): tcp driver registry, identify, preset push delivery

- Track Wi-Fi TCP clients, liveness pings, disconnect broadcast, bind errors via gather\n- Device list/get include connected; POST identify with __identify preset\n- Presets push/send delivery helpers; bump led-driver hello type

Made-with: Cursor

src/models/transport.py

@@ -39,11 +39,13 @@ class SerialSender:
 
         self._serial = serial.Serial(port, baudrate=baudrate, timeout=1)
         self._default_addr = _parse_mac(default_addr)
+        self._write_lock = asyncio.Lock()
 
     async def send(self, data, addr=None):
         mac = _parse_mac(addr) if addr is not None else self._default_addr
         payload = _encode_payload(data)
-        await _to_thread(self._serial.write, mac + payload)
+        async with self._write_lock:
+            await _to_thread(self._serial.write, mac + payload)
         return True