feat(tuning): expose EnrichedTagScale in the tuning lab (#1520)

Promote the enriched-tag weight (#1490) from a taste.Config default into
the DB-backed tuning lab so operators can dial how much folksonomy tags
count vs raw ID3 genre (rule #25).

- Migration 0044: taste_tuning.enriched_tag_scale (DEFAULT 0.5, backfills
  the existing row).
- recsettings: TasteTuning gains the field; seeded/read/updated through
  reconcile + persistTaste; applyTastePatch validates it to [0,1]
  (generic non-half-life clamp) and diffTaste audits it; TasteConfig maps
  it into the profile build.
- API: tasteTuningResp exposes enriched_tag_scale.
- Web tuning card: a data-driven "Enriched tag weight" knob (0 = genre
  only). Tests: recsettings persist+range, web fixture field.

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

internal/db/dbq/recommendation_tuning.sql.go

@@ -10,7 +10,7 @@ import (
 )
 
 const getTasteTuning = `-- name: GetTasteTuning :one
-SELECT singleton, half_life_days, engagement_hard_skip, engagement_neutral, engagement_full, updated_at FROM taste_tuning WHERE singleton = true
+SELECT singleton, half_life_days, engagement_hard_skip, engagement_neutral, engagement_full, updated_at, enriched_tag_scale FROM taste_tuning WHERE singleton = true
 `
 
 func (q *Queries) GetTasteTuning(ctx context.Context) (TasteTuning, error) {
@@ -23,6 +23,7 @@ func (q *Queries) GetTasteTuning(ctx context.Context) (TasteTuning, error) {
 		&i.EngagementNeutral,
 		&i.EngagementFull,
 		&i.UpdatedAt,
+		&i.EnrichedTagScale,
 	)
 	return i, err
 }
@@ -120,9 +121,10 @@ UPDATE taste_tuning
        engagement_hard_skip = $2,
        engagement_neutral   = $3,
        engagement_full      = $4,
+       enriched_tag_scale   = $5,
        updated_at           = now()
  WHERE singleton = true
-RETURNING singleton, half_life_days, engagement_hard_skip, engagement_neutral, engagement_full, updated_at
+RETURNING singleton, half_life_days, engagement_hard_skip, engagement_neutral, engagement_full, updated_at, enriched_tag_scale
 `
 
 type UpdateTasteTuningParams struct {
@@ -130,6 +132,7 @@ type UpdateTasteTuningParams struct {
 	EngagementHardSkip float64
 	EngagementNeutral  float64
 	EngagementFull     float64
+	EnrichedTagScale   float64
 }
 
 func (q *Queries) UpdateTasteTuning(ctx context.Context, arg UpdateTasteTuningParams) (TasteTuning, error) {
@@ -138,6 +141,7 @@ func (q *Queries) UpdateTasteTuning(ctx context.Context, arg UpdateTasteTuningPa
 		arg.EngagementHardSkip,
 		arg.EngagementNeutral,
 		arg.EngagementFull,
+		arg.EnrichedTagScale,
 	)
 	var i TasteTuning
 	err := row.Scan(
@@ -147,6 +151,7 @@ func (q *Queries) UpdateTasteTuning(ctx context.Context, arg UpdateTasteTuningPa
 		&i.EngagementNeutral,
 		&i.EngagementFull,
 		&i.UpdatedAt,
+		&i.EnrichedTagScale,
 	)
 	return i, err
 }
@@ -209,8 +214,8 @@ func (q *Queries) UpdateWeightProfile(ctx context.Context, arg UpdateWeightProfi
 const upsertTasteTuningDefaults = `-- name: UpsertTasteTuningDefaults :exec
 INSERT INTO taste_tuning (
     singleton, half_life_days, engagement_hard_skip,
-    engagement_neutral, engagement_full
-) VALUES (true, $1, $2, $3, $4)
+    engagement_neutral, engagement_full, enriched_tag_scale
+) VALUES (true, $1, $2, $3, $4, $5)
 ON CONFLICT (singleton) DO NOTHING
 `
 
@@ -219,6 +224,7 @@ type UpsertTasteTuningDefaultsParams struct {
 	EngagementHardSkip float64
 	EngagementNeutral  float64
 	EngagementFull     float64
+	EnrichedTagScale   float64
 }
 
 func (q *Queries) UpsertTasteTuningDefaults(ctx context.Context, arg UpsertTasteTuningDefaultsParams) error {
@@ -227,6 +233,7 @@ func (q *Queries) UpsertTasteTuningDefaults(ctx context.Context, arg UpsertTaste
 		arg.EngagementHardSkip,
 		arg.EngagementNeutral,
 		arg.EngagementFull,
+		arg.EnrichedTagScale,
 	)
 	return err
 }