feat(taste): fold enriched folksonomy tags into the profile (#1490 Step 3)

The taste recompute's tag facet now unions the cached track_tags
(MusicBrainz/Last.fm folksonomy tags) alongside raw ID3 genre, so a coarse
"Rock" gains "post-punk / shoegaze / melancholic".

- taste_profile.sql: ListPlayEngagementInputsForUser +
  ListLikedTrackTasteInputsForUser now return track_id to key the
  enriched-tag lookup.
- accumulate(): for each play, fold its track's enriched tags weighted by
  engagement × tag.weight × EnrichedTagScale; for each liked track, by the
  tag-like bonus × tag.weight × scale. A track with no cached tags
  contributes genre only (graceful).
- New Config.EnrichedTagScale (default 0.5) — enriched tags augment the
  ID3 signal without swamping it; 0 = genre-only. Flows through
  recsettings.TasteConfig() (starts from DefaultConfig). Promoting it into
  the admin tuning lab is a small follow-up.

Unit-tested the pure foldEnrichedTags helper (overlap accumulation +
scale=0 disable).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/db/queries/taste_profile.sql

@@ -8,6 +8,7 @@
 -- track duration, clamped to [0,1]); age_days drives the time-decay. Genre
 -- is split into tags in Go. Quarantined tracks are excluded.
 SELECT
+    t.id AS track_id,
     t.artist_id,
     t.genre,
     LEAST(GREATEST(
@@ -25,9 +26,10 @@ WHERE pe.user_id = $1
   );
 
 -- name: ListLikedTrackTasteInputsForUser :many
--- (artist_id, genre) for each track the user has explicitly liked. Feeds the
--- track-like bonus into the liked track's artist and tags.
-SELECT t.artist_id, t.genre
+-- (track_id, artist_id, genre) for each track the user has explicitly
+-- liked. Feeds the track-like bonus into the liked track's artist and
+-- tags; track_id keys the enriched track_tags lookup (#1490).
+SELECT t.id AS track_id, t.artist_id, t.genre
 FROM general_likes gl
 JOIN tracks t ON t.id = gl.track_id
 WHERE gl.user_id = $1;