Add embedded audio/subtitle track selection for multi-track files

Files with multiple embedded tracks (e.g. MKV from media sources or
downloads) previously exposed none of them: mpv's track-list was never
read, aid was never set, and sid was only ever no/auto. The quality
selector showed no Audio or Subtitles tab for such files.

MPVClient now observes track-list/aid/sid and delivers a coalesced,
leniently decoded [MPVTrack] snapshot; selection state is derived from
the reported "selected" flags. Embedded tracks are switched live via
aid/sid (no reload), surfaced in the existing Audio/Subtitles sections
alongside external captions on iOS, tvOS and macOS. External sub-add/
audio-add tracks are filtered out to avoid double-listing. User picks
are sticky across same-video reloads (quality switch, audio mode,
retries) and preferred audio/subtitle languages auto-select a matching
embedded track once per load, with external captions taking precedence.

Yattee/Views/Player/ControlsSectionRenderer.swift

@@ -922,7 +922,8 @@ struct ControlsSectionRenderer: View {
     @ViewBuilder
     private var captionsButton: some View {
         if actions.hasCaptions, actions.onCaptionSelected != nil {
-            controlButton(systemImage: actions.currentCaption != nil ? "captions.bubble.fill" : "captions.bubble") {
+            let subtitlesActive = actions.currentCaption != nil || actions.currentEmbeddedSubtitleTrackID != nil
+            controlButton(systemImage: subtitlesActive ? "captions.bubble.fill" : "captions.bubble") {
                 actions.onShowCaptionsSelector?()
             }
         }