feat(fe): play Discord voice live + fix recording play/download

Voice page (connection tab):
- ListenControl baru: toggle Listen (Headphones) — mulai PcmPlayer dari
  user gesture, subscribe onPcm WS, volume slider, bar level per-user
  REAL dari PCM (bukan random).
- lib/audio/pcm-player.ts (baru): ScriptProcessorNode mixer — ring buffer
  2s per user (hash FNV-1a sama dengan gateway), upsampling 24k→48k
  linear, mix semua user ke mono, gain volume, cleanup ring diam 5s.
- useVoiceListen + hashUserId di hooks; auto-stop saat disconnect.

Recordings:
- recording-player: reset src+load+play() eksplisit (bukan autoPlay doang),
  tampilkan filename + error state 'playback failed' kalau file rusak.
- recording-card: tombol Download fetch blob (CORS tele open) → objectURL
  → force download dengan nama asli; fallback buka tab baru kalau fetch
  gagal; spinner saat mendownload.

Verified: FE tsc 0, next build 10/10 static pages.

services/frontend/src/hooks/index.ts

@@ -34,10 +34,12 @@ export {
   useRecordingsWsSync,
 } from "./use-recordings";
 export {
+  hashUserId,
   useMicTransmit,
   useSpeakers,
   useVoiceChannels,
   useVoiceConnect,
   useVoiceDisconnect,
+  useVoiceListen,
   useVoiceStatus,
 } from "./use-voice";