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/hooks/use-media.ts

@@ -38,6 +38,10 @@ export function useMediaStop() {
   return useMediaAction(() => mediaApi.stop());
 }
 
+export function useMediaLoop() {
+  return useMediaAction((loop: boolean) => mediaApi.loop(loop));
+}
+
 /** Subscribe to WS media_state events to keep cache fresh */
 export function useMediaWsSync(ws: WsHook) {
   const { mutate } = useSWRConfig();