feat(taste): time-of-day / weekday context conditioning — #1531

Milestone #160 Opt 3 (temporal half). A new additive scoring term that
boosts a candidate when its artist's play history concentrates in the
CURRENT daypart × weekday-type cell, in the user's local timezone.

- Migration 0046: recommendation_weight_profiles.context_time_weight
  (per-profile scoring weight, DEFAULT 1.0).
- Query ListArtistContextPlayCountsForUser: per-artist completed-play
  counts split by the current cell (daypart night[22,5)/morning[5,12)/
  afternoon[12,17)/evening[17,22) × weekday-vs-weekend) via
  started_at AT TIME ZONE users.timezone; 365-day window, skips excluded.
- internal/recommendation/context.go: LoadContextAffinity computes each
  artist's shrunk cell-share minus the user's baseline share, clamped to
  [-1,1]; sparse artists shrink toward baseline (pseudo-count 5), unknown
  artists → 0 (cold-start neutral).
- Score() gains context_affinity_score · ContextTimeWeight; both
  candidate loaders set it per candidate.
- Tuning lab: ContextTimeWeight threaded through recsettings + admin API
  + web card ("Time-of-day weight" row) + Go/web tests. Shipped 1.0 both
  profiles (uniform start, re-bakeable).

Device-class axis deferred to #1551 (needs a client_id → device-class
mapping that doesn't exist yet).

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

internal/db/dbq/recommendation_tuning.sql.go

@@ -82,7 +82,7 @@ func (q *Queries) ListTuningAudit(ctx context.Context, limit int32) ([]Recommend
 }
 
 const listWeightProfiles = `-- name: ListWeightProfiles :many
-SELECT profile, base_weight, like_boost, recency_weight, skip_penalty, jitter_magnitude, context_weight, similarity_weight, taste_weight, updated_at FROM recommendation_weight_profiles ORDER BY profile
+SELECT profile, base_weight, like_boost, recency_weight, skip_penalty, jitter_magnitude, context_weight, similarity_weight, taste_weight, updated_at, context_time_weight FROM recommendation_weight_profiles ORDER BY profile
 `
 
 func (q *Queries) ListWeightProfiles(ctx context.Context) ([]RecommendationWeightProfile, error) {
@@ -105,6 +105,7 @@ func (q *Queries) ListWeightProfiles(ctx context.Context) ([]RecommendationWeigh
 			&i.SimilarityWeight,
 			&i.TasteWeight,
 			&i.UpdatedAt,
+			&i.ContextTimeWeight,
 		); err != nil {
 			return nil, err
 		}
@@ -163,29 +164,31 @@ func (q *Queries) UpdateTasteTuning(ctx context.Context, arg UpdateTasteTuningPa
 
 const updateWeightProfile = `-- name: UpdateWeightProfile :one
 UPDATE recommendation_weight_profiles
-   SET base_weight       = $2,
-       like_boost        = $3,
-       recency_weight    = $4,
-       skip_penalty      = $5,
-       jitter_magnitude  = $6,
-       context_weight    = $7,
-       similarity_weight = $8,
-       taste_weight      = $9,
-       updated_at        = now()
+   SET base_weight         = $2,
+       like_boost          = $3,
+       recency_weight      = $4,
+       skip_penalty        = $5,
+       jitter_magnitude    = $6,
+       context_weight      = $7,
+       similarity_weight   = $8,
+       taste_weight        = $9,
+       context_time_weight = $10,
+       updated_at          = now()
  WHERE profile = $1
-RETURNING profile, base_weight, like_boost, recency_weight, skip_penalty, jitter_magnitude, context_weight, similarity_weight, taste_weight, updated_at
+RETURNING profile, base_weight, like_boost, recency_weight, skip_penalty, jitter_magnitude, context_weight, similarity_weight, taste_weight, updated_at, context_time_weight
 `
 
 type UpdateWeightProfileParams struct {
-	Profile          string
-	BaseWeight       float64
-	LikeBoost        float64
-	RecencyWeight    float64
-	SkipPenalty      float64
-	JitterMagnitude  float64
-	ContextWeight    float64
-	SimilarityWeight float64
-	TasteWeight      float64
+	Profile           string
+	BaseWeight        float64
+	LikeBoost         float64
+	RecencyWeight     float64
+	SkipPenalty       float64
+	JitterMagnitude   float64
+	ContextWeight     float64
+	SimilarityWeight  float64
+	TasteWeight       float64
+	ContextTimeWeight float64
 }
 
 func (q *Queries) UpdateWeightProfile(ctx context.Context, arg UpdateWeightProfileParams) (RecommendationWeightProfile, error) {
@@ -199,6 +202,7 @@ func (q *Queries) UpdateWeightProfile(ctx context.Context, arg UpdateWeightProfi
 		arg.ContextWeight,
 		arg.SimilarityWeight,
 		arg.TasteWeight,
+		arg.ContextTimeWeight,
 	)
 	var i RecommendationWeightProfile
 	err := row.Scan(
@@ -212,6 +216,7 @@ func (q *Queries) UpdateWeightProfile(ctx context.Context, arg UpdateWeightProfi
 		&i.SimilarityWeight,
 		&i.TasteWeight,
 		&i.UpdatedAt,
+		&i.ContextTimeWeight,
 	)
 	return i, err
 }
@@ -249,21 +254,23 @@ const upsertWeightProfileDefaults = `-- name: UpsertWeightProfileDefaults :exec
 
 INSERT INTO recommendation_weight_profiles (
     profile, base_weight, like_boost, recency_weight, skip_penalty,
-    jitter_magnitude, context_weight, similarity_weight, taste_weight
-) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
+    jitter_magnitude, context_weight, similarity_weight, taste_weight,
+    context_time_weight
+) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
 ON CONFLICT (profile) DO NOTHING
 `
 
 type UpsertWeightProfileDefaultsParams struct {
-	Profile          string
-	BaseWeight       float64
-	LikeBoost        float64
-	RecencyWeight    float64
-	SkipPenalty      float64
-	JitterMagnitude  float64
-	ContextWeight    float64
-	SimilarityWeight float64
-	TasteWeight      float64
+	Profile           string
+	BaseWeight        float64
+	LikeBoost         float64
+	RecencyWeight     float64
+	SkipPenalty       float64
+	JitterMagnitude   float64
+	ContextWeight     float64
+	SimilarityWeight  float64
+	TasteWeight       float64
+	ContextTimeWeight float64
 }
 
 // Recommendation tuning lab queries (#1250). Seeding happens via the
@@ -281,6 +288,7 @@ func (q *Queries) UpsertWeightProfileDefaults(ctx context.Context, arg UpsertWei
 		arg.ContextWeight,
 		arg.SimilarityWeight,
 		arg.TasteWeight,
+		arg.ContextTimeWeight,
 	)
 	return err
 }