Add audio-only music mode

Persistent per-platform mode that plays only the audio track to save
bandwidth and speed up loads. When enabled, stream selection picks the
best audio-only stream (preferred language, codec, bitrate) and never
fetches the video URL; toggling mid-video reloads at the current
position using the quality-switch path (live vid=no toggling is avoided
due to A/V desync).

- Toggle row in the player quality/settings sheet on iOS, macOS and
  tvOS, next to lock controls
- New audioMode control button type (red when active) for player
  controls and mini player layouts
- Picking a video quality explicitly turns the mode off; audio track
  picks keep it on and now work while audio-only is playing
- Stream URL refresh preserves audio-only playback instead of
  resurrecting video
- Queue preloads and history entries resolved before a toggle are
  discarded so selection re-runs with the current mode
- tvOS player shows the video thumbnail instead of a black screen
  during audio-only playback
- PiP button hidden for audio-only streams

Yattee/Views/Player/macOS/MacOSControlsSectionRenderer.swift

@@ -271,6 +271,19 @@ struct MacOSControlsSectionRenderer: View {
                 .opacity(isLocked ? 0.5 : 1.0)
             }
 
+        case .audioMode:
+            if actions.onToggleAudioMode != nil {
+                controlButton(
+                    systemImage: "music.note",
+                    tint: actions.isAudioModeEnabled ? .red : tint,
+                    help: config.buttonType.displayName
+                ) {
+                    actions.onToggleAudioMode?()
+                }
+                .disabled(isLocked)
+                .opacity(isLocked ? 0.5 : 1.0)
+            }
+
         case .seek:
             if let settings = config.seekSettings {
                 seekButton(settings: settings, config: config)