feat(media): loop mode + high-quality OggOpus music playback

- Loop: toggle via POST /api/media/loop → COMMAND_MEDIA_LOOP; gateway
  replays finished music track on natural end (queue untouched); status
  payload exposes loop flag; FE tombol Loop di music-player + mini-player.
- Kualitas suara: music playback sekarang di-transcode sekali via ffmpeg ke
  OggOpus 48kHz stereo 192kbps dengan volume di-bake ke encode — menghindari
  double lossy encode (inlineVolume) yang bikin suara buram. Screen share
  tetap pakai jalur lama.
- Backend: MediaState.loop, setLoop service, route + schema validation.

services/frontend/src/lib/api/media.ts

@@ -7,4 +7,5 @@ export const mediaApi = {
     api.post<MediaState>("/api/media/queue", { source, mode }),
   skip: () => api.post<MediaState>("/api/media/skip", {}),
   stop: () => api.post<MediaState>("/api/media/stop", {}),
+  loop: (loop: boolean) => api.post<MediaState>("/api/media/loop", { loop }),
 };