fix: use getattr for ws.closed compatibility with websockets API

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

relay.py

@@ -237,7 +237,7 @@ class Relay:
 
     async def _on_speaker_frame(self, pcm_bytes):
         """Receive speaker PCM from bridge, resample, encode Opus, send to ESP32."""
-        if not self.ws or self.ws.closed:
+        if not self.ws or getattr(self.ws, 'closed', False):
             return
         try:
             self._audio_out_count += 1