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/database/sql/queries/release_groups.sql

@@ -64,6 +64,17 @@ SELECT
     COALESCE(rg.year, 0) AS release_year,
     rg.mbid,
     COALESCE(ac.text, fallback_ac.text, '') as artist_name,
+    -- primary (first-credited) album artist's MBID, for linking the
+    -- artist name to its detail page.  Empty when the album has no
+    -- MB-tagged album-artist credit.
+    CAST(COALESCE((
+        SELECT a.mbid
+        FROM artist_credit_artist aca_p
+        JOIN artists a ON a.id = aca_p.artist_id
+        WHERE aca_p.credit_id = rg.album_artist_credit_id
+        ORDER BY aca_p.id
+        LIMIT 1
+    ), '') AS TEXT) as artist_mbid,
     COALESCE(ca.file_path, '') as cover_art_path
 FROM release_groups rg
 LEFT JOIN artist_credit ac ON rg.album_artist_credit_id = ac.id
@@ -89,6 +100,17 @@ SELECT
     COALESCE(rg.year, 0) AS release_year,
     rg.mbid,
     COALESCE(ac.text, fallback_ac.text, '') as artist_name,
+    -- primary (first-credited) album artist's MBID, for linking the
+    -- artist name to its detail page.  Empty when the album has no
+    -- MB-tagged album-artist credit.
+    CAST(COALESCE((
+        SELECT a.mbid
+        FROM artist_credit_artist aca_p
+        JOIN artists a ON a.id = aca_p.artist_id
+        WHERE aca_p.credit_id = rg.album_artist_credit_id
+        ORDER BY aca_p.id
+        LIMIT 1
+    ), '') AS TEXT) as artist_mbid,
     COALESCE(ca.file_path, '') as cover_art_path
 FROM release_groups rg
 LEFT JOIN artist_credit ac ON rg.album_artist_credit_id = ac.id
@@ -116,6 +138,17 @@ SELECT
     COALESCE(rg.original_year, rg.year) AS year,
     COALESCE(rg.year, 0) AS release_year,
     COALESCE(ac.text, fallback_ac.text, '') as artist_name,
+    -- primary (first-credited) album artist's MBID, for linking the
+    -- artist name to its detail page.  Empty when the album has no
+    -- MB-tagged album-artist credit.
+    CAST(COALESCE((
+        SELECT a.mbid
+        FROM artist_credit_artist aca_p
+        JOIN artists a ON a.id = aca_p.artist_id
+        WHERE aca_p.credit_id = rg.album_artist_credit_id
+        ORDER BY aca_p.id
+        LIMIT 1
+    ), '') AS TEXT) as artist_mbid,
     COALESCE(ca.file_path, '') as cover_art_path
 FROM release_groups rg
 JOIN artist_credit ac ON rg.album_artist_credit_id = ac.id
@@ -141,6 +174,17 @@ SELECT
     COALESCE(rg.original_year, rg.year) AS year,
     COALESCE(rg.year, 0) AS release_year,
     COALESCE(ac.text, fallback_ac.text, '') as artist_name,
+    -- primary (first-credited) album artist's MBID, for linking the
+    -- artist name to its detail page.  Empty when the album has no
+    -- MB-tagged album-artist credit.
+    CAST(COALESCE((
+        SELECT a.mbid
+        FROM artist_credit_artist aca_p
+        JOIN artists a ON a.id = aca_p.artist_id
+        WHERE aca_p.credit_id = rg.album_artist_credit_id
+        ORDER BY aca_p.id
+        LIMIT 1
+    ), '') AS TEXT) as artist_mbid,
     COALESCE(ca.file_path, '') as cover_art_path
 FROM release_groups rg
 JOIN artist_credit ac ON rg.album_artist_credit_id = ac.id