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>

web/src/lib/api/tuning.ts

@@ -13,6 +13,7 @@ export type WeightProfile = {
   context_weight: number;
   similarity_weight: number;
   taste_weight: number;
+  context_time_weight: number;
 };
 
 export type TasteTuning = {

web/src/routes/admin/tuning/+page.svelte

@@ -29,7 +29,8 @@
     { key: 'jitter_magnitude',  label: 'Jitter',            hint: 'Random reshuffle magnitude for near-ties.' },
     { key: 'context_weight',    label: 'Context weight',    hint: 'Session-vector similarity contribution.' },
     { key: 'similarity_weight', label: 'Similarity weight', hint: 'Seed-similarity contribution.' },
-    { key: 'taste_weight',      label: 'Taste weight',      hint: 'Learned taste-profile fit, in [-1, +1].' }
+    { key: 'taste_weight',      label: 'Taste weight',      hint: 'Learned taste-profile fit, in [-1, +1].' },
+    { key: 'context_time_weight', label: 'Time-of-day weight', hint: "Artist's time-of-day/weekday affinity for the current context, in [-1, +1]. 0 = ignore when you listen." }
   ];
 
   const tasteFields: { key: keyof TasteTuning; label: string; hint: string }[] = [

web/src/routes/admin/tuning/tuning.test.ts

@@ -28,6 +28,7 @@ const weights = (over: Partial<Record<string, number>> = {}) => ({
   context_weight: 0.5,
   similarity_weight: 1.5,
   taste_weight: 1.5,
+  context_time_weight: 1,
   ...over
 });