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/components/config-page/config-page.ts

@@ -1945,7 +1945,7 @@ export class ConfigPage extends LitElement {
         return html`
             <config-section
                 heading="Search Index"
-                description="The explore search index pre-caches popular artists, albums, and tracks from ListenBrainz for fast offline search."
+                description="The explore search index is built from the MusicBrainz/ListenBrainz data dumps — popular artists, albums, and tracks with listen counts — for fast offline search."
                 .open=${true}
             >
                 <div class="index-status">