Backend:
- Added mbid column to sqlc schemas for artists and release_groups
- Regenerated sqlc queries to SELECT mbid in artist/album queries
- Added MBID field to library.Artist and library.Album Go structs
- All GetAllArtists/GetAllAlbums variants now populate MBID
Frontend:
- Updated Wails models.ts with MBID fields on Artist and Album
- Added cachedArtists/cachedAlbums getters to LibraryStore
- searchLibraryCache now includes MBIDs and local cover art URLs
so library results can navigate to explore detail pages
- Added mergeWithLibrary() — when full MB results arrive, library
entries are enriched with local images and 'In Library' flags
rather than being replaced by MB-only versions
- Created ExploreCache store for cross-page data sharing: search
results populate the cache, detail pages can read from it to
avoid redundant API calls for already-fetched data