feat(taste): mood taste facet — #1534

Milestone #160 Opt 2b (mood half of the era+mood option). A fourth taste
facet alongside artists + genre tags + eras: signed weights over canonical
mood buckets (melancholic / energetic / chill / …) derived from a track's
enriched folksonomy tags (#1490).

- internal/mood: shared vocabulary — Of(tags) maps folksonomy tags to
  canonical mood buckets (synonyms collapse). Imported by both the taste
  builder and the scorer so a track's mood is derived identically.
- Migration 0047: taste_profile_moods table + taste_tuning.mood_scale
  (DEFAULT 0.5).
- Build side (internal/taste): Config.MoodScale ([0,1] damper, mirrors
  EraScale); accumulate folds each play/like's mood buckets at
  base*MoodScale; persist atomic-replaces the mood rows.
- Scorer (internal/recommendation): TasteProfile gains a mood term
  (own tanh scale + additive 0.12 share, so it never weakens the existing
  signal when a track has no mood tags). Match now takes the candidate's
  mood buckets; loaded per candidate (ListTrackTagsForTracks → mood.Of) in
  the primary similarity loader only — the near-whole-library fallback
  pool passes nil (mood → 0) to avoid a full-library tag scan.
- Tuning lab: mood_scale threaded through recsettings + admin API + web
  card ("Mood weight" row) + Go/web tests.

Coverage is partial (grows with tag enrichment; richer once Last.fm is
keyed), so mood is a supplement — neutral for tracks with no mood tags.

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

internal/db/dbq/taste_profile.sql.go

@@ -29,6 +29,15 @@ func (q *Queries) DeleteTasteProfileErasForUser(ctx context.Context, userID pgty
 	return err
 }
 
+const deleteTasteProfileMoodsForUser = `-- name: DeleteTasteProfileMoodsForUser :exec
+DELETE FROM taste_profile_moods WHERE user_id = $1
+`
+
+func (q *Queries) DeleteTasteProfileMoodsForUser(ctx context.Context, userID pgtype.UUID) error {
+	_, err := q.db.Exec(ctx, deleteTasteProfileMoodsForUser, userID)
+	return err
+}
+
 const deleteTasteProfileTagsForUser = `-- name: DeleteTasteProfileTagsForUser :exec
 DELETE FROM taste_profile_tags WHERE user_id = $1
 `
@@ -70,6 +79,22 @@ func (q *Queries) InsertTasteProfileEra(ctx context.Context, arg InsertTasteProf
 	return err
 }
 
+const insertTasteProfileMood = `-- name: InsertTasteProfileMood :exec
+INSERT INTO taste_profile_moods (user_id, mood, weight)
+VALUES ($1, $2, $3)
+`
+
+type InsertTasteProfileMoodParams struct {
+	UserID pgtype.UUID
+	Mood   string
+	Weight float64
+}
+
+func (q *Queries) InsertTasteProfileMood(ctx context.Context, arg InsertTasteProfileMoodParams) error {
+	_, err := q.db.Exec(ctx, insertTasteProfileMood, arg.UserID, arg.Mood, arg.Weight)
+	return err
+}
+
 const insertTasteProfileTag = `-- name: InsertTasteProfileTag :exec
 INSERT INTO taste_profile_tags (user_id, tag, weight)
 VALUES ($1, $2, $3)
@@ -304,6 +329,45 @@ func (q *Queries) ListTasteProfileErasForUser(ctx context.Context, arg ListTaste
 	return items, nil
 }
 
+const listTasteProfileMoodsForUser = `-- name: ListTasteProfileMoodsForUser :many
+SELECT mood, weight
+FROM taste_profile_moods
+WHERE user_id = $1
+ORDER BY weight DESC
+LIMIT $2
+`
+
+type ListTasteProfileMoodsForUserParams struct {
+	UserID pgtype.UUID
+	Limit  int32
+}
+
+type ListTasteProfileMoodsForUserRow struct {
+	Mood   string
+	Weight float64
+}
+
+// Top-weighted taste moods (#1534); consumed by the scorer's mood term.
+func (q *Queries) ListTasteProfileMoodsForUser(ctx context.Context, arg ListTasteProfileMoodsForUserParams) ([]ListTasteProfileMoodsForUserRow, error) {
+	rows, err := q.db.Query(ctx, listTasteProfileMoodsForUser, arg.UserID, arg.Limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListTasteProfileMoodsForUserRow
+	for rows.Next() {
+		var i ListTasteProfileMoodsForUserRow
+		if err := rows.Scan(&i.Mood, &i.Weight); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const listTasteProfileTagsForUser = `-- name: ListTasteProfileTagsForUser :many
 SELECT tag, weight
 FROM taste_profile_tags