feat: autotag scoring overhaul, dump-based explore index, and lyrics search

Consolidates in-progress work across autotag, explore, and library:

- autotag: beets/Picard-informed scoring engine — ID-first matching, VA
  handling, recommendation tiers, and a merged distance/rank cascade, with
  an eval harness for regression tracking.
- explore: offline MusicBrainz dump import/incremental refresh replaces the
  legacy tier crawl; index-first local search with fuzzy matching and a
  dedicated ranker; disk-free guards for dump downloads.
- library: artist-credit extraction and matching.
- lyrics: owned-library lyric search (FTS) with LRCLIB backfill.

Also: rewrite README to be user-focused, and migrate upstream to
git.ljones.me/yonlu/yellowjacket.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/library/crud.go

@@ -37,6 +37,9 @@ type RemovalHooks struct {
 	StopPlayback func()
 	// CompactQueue reloads queue state after cascade deletes.
 	CompactQueue func()
+	// PostRemove runs after the removal commits, for cross-cutting
+	// invalidation (e.g. clearing library-sync "ready" markers).
+	PostRemove func()
 }
 
 // SetRemovalHooks provides optional hooks for cross-cutting
@@ -461,6 +464,12 @@ func (l *Library) RemoveLibrary(id int64) (*RemovalSummary, error) {
 		l.removalHooks.CompactQueue()
 	}
 
+	// 22. Post-commit: invalidate library-sync markers so the gated
+	// index/lyric re-sync runs on the next launch.
+	if l.removalHooks.PostRemove != nil {
+		l.removalHooks.PostRemove()
+	}
+
 	summary := &RemovalSummary{
 		TracksDeleted:     tracksDeleted,
 		ArtistsRemoved:    artistsRemoved,