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/dbq/taste_profile.sql.go

@@ -87,19 +87,21 @@ func (q *Queries) ListLikedArtistIDsForUser(ctx context.Context, userID pgtype.U
 }
 
 const listLikedTrackTasteInputsForUser = `-- name: ListLikedTrackTasteInputsForUser :many
-SELECT t.artist_id, t.genre
+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
 `
 
 type ListLikedTrackTasteInputsForUserRow struct {
+	TrackID  pgtype.UUID
 	ArtistID pgtype.UUID
 	Genre    *string
 }
 
-// (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, 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).
 func (q *Queries) ListLikedTrackTasteInputsForUser(ctx context.Context, userID pgtype.UUID) ([]ListLikedTrackTasteInputsForUserRow, error) {
 	rows, err := q.db.Query(ctx, listLikedTrackTasteInputsForUser, userID)
 	if err != nil {
@@ -109,7 +111,7 @@ func (q *Queries) ListLikedTrackTasteInputsForUser(ctx context.Context, userID p
 	var items []ListLikedTrackTasteInputsForUserRow
 	for rows.Next() {
 		var i ListLikedTrackTasteInputsForUserRow
-		if err := rows.Scan(&i.ArtistID, &i.Genre); err != nil {
+		if err := rows.Scan(&i.TrackID, &i.ArtistID, &i.Genre); err != nil {
 			return nil, err
 		}
 		items = append(items, i)
@@ -123,6 +125,7 @@ func (q *Queries) ListLikedTrackTasteInputsForUser(ctx context.Context, userID p
 const listPlayEngagementInputsForUser = `-- name: ListPlayEngagementInputsForUser :many
 
 SELECT
+    t.id AS track_id,
     t.artist_id,
     t.genre,
     LEAST(GREATEST(
@@ -146,6 +149,7 @@ type ListPlayEngagementInputsForUserParams struct {
 }
 
 type ListPlayEngagementInputsForUserRow struct {
+	TrackID    pgtype.UUID
 	ArtistID   pgtype.UUID
 	Genre      *string
 	Completion float64
@@ -169,6 +173,7 @@ func (q *Queries) ListPlayEngagementInputsForUser(ctx context.Context, arg ListP
 	for rows.Next() {
 		var i ListPlayEngagementInputsForUserRow
 		if err := rows.Scan(
+			&i.TrackID,
 			&i.ArtistID,
 			&i.Genre,
 			&i.Completion,

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;