Implement the audio_service media-browser hooks so Android Auto (and other
media browsers) can browse the library and start playback:
- getChildren exposes Liked Songs, a "Browse" folder (the home / "Made for
you" hub — including Discover Weekly, fetched via browse.sectionItems since
the section preview omits it), and the user's saved playlists.
- Collections are browsable into their track list with a "Play all" entry;
tapping a track plays the collection from that point.
- playFromMediaId resolves the selection and plays through the existing
AudioPlayerNotifier.load pipeline.
- Add an explicit shuffle MediaControl + custom action (Android Auto does not
reliably render a toggle from the standard ACTION_SET_SHUFFLE_MODE alone).
- Retry auth-sensitive requests: the stored token is often stale on cold
start and the first call 401s before the plugin refreshes it.
- Browse-item artwork uses http(s) URLs only — the media-browser process
cannot read app-private file:// paths.
The MediaBrowserService and automotive_app_desc.xml were already declared in
the manifest, so no native changes are required.
