Adds the Riverpod provider (constructed with dioFactory pulling from
the authenticated dioProvider) and extends PlayerActions.playTracks
to forward the cache to audio_handler.configure(). The handler
signature change lands in the next commit.
Intentional intermediate-broken state: audio_handler.configure
doesn't yet accept coverCache. Resolved by the next task in the same
push.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
audio_service runs the handler in a background isolate; UI watches
playbackState/mediaItem/queue streams through Riverpod. AndroidManifest
gets the foreground-service media-playback permission; Info.plist gets
UIBackgroundModes=audio. Bearer token attached to stream URLs via
just_audio's per-source headers.
bvandeusen