MetadataPrefetcher gains warmAlbums(ids) / warmArtists(ids) public
methods so callers can fan out drift-cache warm-ups for whatever
collection just landed.
Wired into:
- Library Artists tab — warms first 8 artists from the page on every
data emit (initial + paginate + refresh).
- Library Albums tab — same for first 8 albums.
- Artist detail album grid — warms first 8 albums from the artist's
album list as soon as it loads, so tapping into any of them is a
drift hit.
Hard-cap of 8 per call (same as the home prefetch). Set spans across
calls aren't deduped at this layer because providers themselves
short-circuit on cached values.
Also instrument the artist-detail play button: try/catch around the
artistTracksProvider read + playTracks call, snackbar on
empty-tracks or thrown-error so silent failures stop being silent.
The current behavior was an early return on tracks.isEmpty with no
visible feedback.