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>

frontend/src/events.ts

@@ -63,6 +63,9 @@ export const Events = {
 
     // Explore / search index events
     IndexStatusChanged: "IndexStatusChanged",
+    ArtistDiscographyReady: "ArtistDiscographyReady",
+    ArtistSimilarReady: "ArtistSimilarReady",
+    AlbumReleasesReady: "AlbumReleasesReady",
 } as const;
 
 export type EventName = (typeof Events)[keyof typeof Events];