fix(win): stop Disconnect from freezing the UI, and a 100% CPU spin on link loss

[ssuyash3000]

Three related problems around teardown on Windows:

1. BluetoothWrapper::disconnect() took _connectorMtx before closing the
   socket, but a worker thread holds that same lock while blocked in recv().
   Closing the socket is what releases that thread, so the UI thread waited on
   the lock — Disconnect froze the window until the 2.5s recv timeout expired,
   and closing the app while a read was in flight hung it. On Windows, close
   first, then take the lock; other platforms keep the old order.

2. _socket was written by the UI thread (disconnect) while a worker thread
   read it inside send()/recv() — a data race that could hand recv() a
   closed or recycled handle. It is now std::atomic<SOCKET>, swapped through
   a single _closeSocket().

3. recv() returning 0 (graceful close by the headphones) was treated as a
   successful read of an empty buffer, so BluetoothWrapper::_readMessage()
   looped forever looking for a start marker — one core pegged until the app
   was killed. Both the connector and the wrapper now treat it as a
   disconnect.

Also loops send() until the whole frame is out: a partial send left the
device waiting for the rest of a command that never arrived.