feat(music): mpv audio playback engine with gapless queue service

Audio-only mpv core on every platform (dedicated
com.plezy/mpv_audio_player channels): parameterized android/windows/
linux mpv plugins and a new apple MpvAudioPlayerCore, all skipping
video/window paths (vid=no, audio-display=no, gapless-audio=weak).
MusicPlaybackService drives an in-memory queue with shuffle/repeat,
file-loaded-event gapless arming (property edges coalesce and the
android bridge drops them), per-track progress reporting, OS media
controls, audio focus, sleep timer, and error auto-skip.
PlaybackCoordinator enforces one live native player: starting video
disposes the audio core first.

tvos/Runner/AppDelegate.swift

@@ -138,6 +138,9 @@ import wakelock_plus
     if let r = self.registrar(forPlugin: "MpvPlayerPlugin") {
       MpvPlayerPlugin.register(with: r)
     }
+    if let r = self.registrar(forPlugin: "MpvAudioPlayerPlugin") {
+      MpvAudioPlayerPlugin.register(with: r)
+    }
     if let r = self.registrar(forPlugin: "AtmosProbePlugin") {
       AtmosProbePlugin.register(with: r)
     }