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/PlayerControlsView.swift

@@ -382,6 +382,7 @@ struct PlayerControlsView: View {
             panscanValue: panscanValue,
             isPanscanAllowed: isPanscanAllowed,
             isAutoPlayNextEnabled: appEnvironment?.settingsManager.queueAutoPlayNext ?? true,
+            isAudioModeEnabled: appEnvironment?.settingsManager.audioOnlyModeEnabled ?? false,
             yatteeServerURL: appEnvironment?.instancesManager.yatteeServerInstances.first { $0.isEnabled }?.url,
             deArrowBrandingProvider: appEnvironment?.deArrowBrandingProvider,
             onClose: onClose,
@@ -395,6 +396,11 @@ struct PlayerControlsView: View {
             onToggleAutoPlayNext: {
                 appEnvironment?.settingsManager.queueAutoPlayNext.toggle()
             },
+            onToggleAudioMode: { [weak appEnvironment] in
+                guard let appEnvironment else { return }
+                let enabled = !appEnvironment.settingsManager.audioOnlyModeEnabled
+                Task { await appEnvironment.playerService.setAudioMode(enabled) }
+            },
             onShowSettings: onShowSettings,
             onPlayNext: onPlayNext,
             onPlayPrevious: onPlayPrevious,