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-types.ts

@@ -6,12 +6,14 @@ export interface HistoryVideoRow {
   parsedEpisode: number | null;
   animeTitle: string | null;
   lastWatchedMs: number;
+  coverBlobHash: string | null;
 }
 
 export interface HistorySeriesEntry {
   seriesRoot: string;
   displayName: string;
   lastWatched: HistoryVideoRow;
+  coverBlobHash: string | null;
 }
 
 export interface SeasonDirEntry {