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/backend/src/modules/media/media.schema.ts

@@ -5,4 +5,9 @@ export const mediaQueueSchema = z.object({
   mode: z.enum(["music", "screen"]).default("music"),
 });
 
+export const mediaLoopSchema = z.object({
+  loop: z.boolean().default(false),
+});
+
 export type MediaQueueInput = z.infer<typeof mediaQueueSchema>;
+export type MediaLoopInput = z.infer<typeof mediaLoopSchema>;