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/types.ts

@@ -42,7 +42,6 @@ export interface SegmentMetadata extends UserMetadata {
 
 export interface PcmBroadcaster {
   broadcastPcmToWeb?: (chunk: Buffer, userId: string) => void;
-  broadcastOpusToWeb?: (chunk: Buffer, userId: string) => void;
   updateActiveUser?: (
     userId: string,
     data: { username: string; avatar: string; speaking: boolean },