feat(launcher): show cover art icons in rofi history picker

- Add history-art.ts: materializeCoverArt extracts cover blobs from stats DB to ~/.cache/subminer/covers
- Query cover_blob_hash in history-db with fallback via shared anime_id
- Backfill cover hash from older rows of the same series in groupHistoryBySeries
- Pass icons to rofi via null-separator protocol (\0icon\x1f<path>)

launcher/history.ts

@@ -1,3 +1,4 @@
+export * from './history-art.js';
 export * from './history-db.js';
 export * from './history-navigation.js';
 export type { HistorySeriesEntry, HistoryVideoRow, SeasonDirEntry } from './history-types.js';