feat(tuning): scoring weights → DB-backed admin tuning lab

The recommendation scoring knobs move out of YAML (radio profile) and
out of the systemMixWeights hard-code (daily_mix profile) into
DB-backed settings with live effect (#1250) — the defaults-discovery
lab per decision #1247: the operator turns knobs to find good values,
which then get baked back into shipped defaults; end users and other
operators should never need the card.

- Migration 0040: recommendation_weight_profiles (radio / daily_mix,
  8 weight columns), taste_tuning singleton (engagement half-life +
  completion-curve points), recommendation_tuning_audit (one row per
  change with a {field, old, new} diff — the trend view's markers,
  #1251).
- internal/recsettings: boot reconcile seeds shipped defaults without
  clobbering tuned rows (coverart SettingsService pattern), validates
  patches (bounds, curve ordering), writes audit rows, and pushes
  daily_mix weights + taste config into package playlists. No-op
  patches write no audit row.
- playlists gains SetSystemMixWeights / SetTasteConfig swap points
  under a RWMutex — no signature threading through the producers; the
  scheduler's taste rebuild reads the pushed config.
- Radio reads its weight profile from the service per request; the 8
  weight fields leave config.RecommendationConfig (YAML keeps only
  RecentlyPlayedHours / RadioSize / RadioSizeMax).
- Admin API: GET/PATCH/reset under /api/admin/recommendation-tuning,
  echoing current + shipped values.
- Web: new admin Tuning tab — two weight profiles side by side, taste
  card, per-scope save (changed fields only) + reset, deviation dots
  against shipped defaults.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TsF3cNoKrqCYsU78cXC8U6

web/src/lib/api/tuning.ts

@@ -0,0 +1,49 @@
+import { api } from './client';
+
+// Mirrors internal/api/admin_recommendation_tuning.go (#1250): the
+// recommendation tuning lab. Field names are the server's snake_case
+// keys, used verbatim in PATCH bodies.
+
+export type WeightProfile = {
+  base_weight: number;
+  like_boost: number;
+  recency_weight: number;
+  skip_penalty: number;
+  jitter_magnitude: number;
+  context_weight: number;
+  similarity_weight: number;
+  taste_weight: number;
+};
+
+export type TasteTuning = {
+  half_life_days: number;
+  engagement_hard_skip: number;
+  engagement_neutral: number;
+  engagement_full: number;
+};
+
+export type TuningScope = 'radio' | 'daily_mix' | 'taste';
+
+export type TuningSnapshot = {
+  profiles: Record<'radio' | 'daily_mix', WeightProfile>;
+  taste: TasteTuning;
+  shipped: {
+    profiles: Record<'radio' | 'daily_mix', WeightProfile>;
+    taste: TasteTuning;
+  };
+};
+
+export function getTuning(): Promise<TuningSnapshot> {
+  return api.get<TuningSnapshot>('/api/admin/recommendation-tuning');
+}
+
+export function patchTuning(
+  scope: TuningScope,
+  values: Record<string, number>
+): Promise<TuningSnapshot> {
+  return api.patch<TuningSnapshot>(`/api/admin/recommendation-tuning/${scope}`, { values });
+}
+
+export function resetTuning(scope: TuningScope): Promise<TuningSnapshot> {
+  return api.post<TuningSnapshot>(`/api/admin/recommendation-tuning/${scope}/reset`, {});
+}