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>

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

@@ -36,7 +36,8 @@
     { key: 'half_life_days',       label: 'Half-life (days)', hint: "A play's influence halves every this-many days." },
     { key: 'engagement_hard_skip', label: 'Hard-skip point',  hint: 'Completion at/below which a play reads −1.' },
     { key: 'engagement_neutral',   label: 'Neutral point',    hint: 'Completion at which a play reads 0.' },
-    { key: 'engagement_full',      label: 'Full point',       hint: 'Completion at/above which a play reads +1.' }
+    { key: 'engagement_full',      label: 'Full point',       hint: 'Completion at/above which a play reads +1.' },
+    { key: 'enriched_tag_scale',   label: 'Enriched tag weight', hint: 'How much folksonomy tags (MusicBrainz/Last.fm) count vs raw file genre, in [0, 1]. 0 = genre only.' }
   ];
 
   const profileScopes: { scope: 'radio' | 'daily_mix'; label: string; blurb: string }[] = [

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

@@ -36,6 +36,7 @@ const taste = (over: Partial<Record<string, number>> = {}) => ({
   engagement_hard_skip: 0.05,
   engagement_neutral: 0.3,
   engagement_full: 0.9,
+  enriched_tag_scale: 0.5,
   ...over
 });