Add low-latency volume control via WebSocket

- Send volume updates through WebSocket instead of HTTP POST
- Reduce throttle from 50ms to 16ms (~60 updates/sec)
- Fall back to HTTP if WebSocket is disconnected

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

media_server/routes/media.py

@@ -309,6 +309,12 @@ async def websocket_endpoint(
                     "type": "status",
                     "data": status_data.model_dump(),
                 })
+            elif data.get("type") == "volume":
+                # Low-latency volume control via WebSocket
+                volume = data.get("volume")
+                if volume is not None:
+                    controller = get_media_controller()
+                    await controller.set_volume(int(volume))
 
     except WebSocketDisconnect:
         await ws_manager.disconnect(websocket)