Replace per-card GetThumbnail calls (10 round-trips) with a single
GetThumbnails batch call that fetches all visible album thumbnails
in one Wails bridge round-trip.
Backend GetThumbnails accepts []ThumbnailRequest and returns
map[mbid]→dataURL. Each request still checks library → disk cache
→ CAA in order, but the bridge overhead is 1 call instead of 10.
Frontend fires loadThumbnails() once after search results arrive.
Album cards render immediately with CAA URL fallback, then re-render
once the batch resolves with cached/local data URLs.
yonlu
0e376abfbb