8ae447e08d
Replace the labelled availability/metadata badges in track rows with small icon+tooltip indicators (cloud/hard-drives/warning/etc, derived from TrackAvailability and MetadataStatus). Add a `connection` slice fed by a single status poller (Sidebar) so other components can cheaply check backend reachability. TrackRow uses this plus the offline audio cache to show "Local" instead of a stale "On server" when the backend is down but the track is already cached.