revert: simplify listen to PCM-only, remove WebCodecs complexity

- Remove broadcastOpusToWeb from types and webserver
- Revert recorder to PCM-only broadcast path
- Remove WebCodecs AudioDecoder from dashboard.js
- Simplify WebSocket handler to just play PCM frames
- Remove Howler.js and Tone.js dependencies
- Keep simple AudioContext playback that works reliably

src/recorder.ts

@@ -176,7 +176,6 @@ export async function startRecording(
         onPacket: (chunk) => {
           if (chunk.length < 8) return;
           segmentManager.rotateIfNeeded(oggPacketStream);
-          broadcaster.broadcastOpusToWeb?.(chunk, userId);
           if (!broadcaster.broadcastPcmToWeb) return;
           decoder.rotateIfNeeded();
           decoder.write(chunk);