feat(gamification): Phase 1 — full kill-switch + textbook XP wrapping

Until now the 'gamification' feature flag did nothing: it had no row in
app_settings, the admin couldn't toggle it, awardXP/awardCoins ignored
it, and the CSS only hid three dashboard widgets — XP bars in textbooks
stayed visible regardless.

Phase 1 closes every hole.

Backend (source of truth):
  • migration 029 seeds feature_gamification_enabled=1
  • new isGamificationEnabled() helper in gamification/_shared.js with a
    30s cache + invalidateGamificationCache() for instant admin toggles
  • awardXP / awardCoins / updateStreak / unlockAchievement /
    checkAchievements all bail out when the flag is off
  • /api/gamification/* and /api/shop/* (user routes) return 404 when
    disabled; admin routes remain open so the switch itself is reachable
  • adminController.updateFeatures gains 'gamification' in the allow-list
    and invalidates the cache on flip

Frontend:
  • LS.isGamificationEnabled() (synchronous, populated by loadFeatures)
    so xp.js + applyCosmetics can bail without a round-trip
  • xp.js load/add/flush become no-ops when the flag is off
  • applyCosmetics skips the round-trip when off
  • CSS .no-gamification rule expanded to cover .hero-xp-badge, .po-xp,
    .xp-card, .xp-bar, #frames-section, and a universal [data-gamified]
    hook for future blocks

Textbooks (Variant 2 of the plan):
  • backend/scripts/wrap_textbook_xp.py — idempotent script that adds
    data-gamified to 167 XP tags across 63 textbook files (chapters +
    hubs, all subjects/grades). Single CSS rule now hides everything.

Verified end-to-end: with the flag off, awardXP/awardCoins write nothing;
flipping back restores normal behavior.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/css/ls.css

@@ -1017,13 +1017,33 @@ body {
 /* Student without a class: hide leaderboard */
 body.no-class #lb-section { display: none !important; }
 
+/* Gamification kill-switch.
+   When admin turns off the feature, body.no-gamification is set by
+   api.js/hideDisabledFeatures and EVERY XP / coin / streak / shop /
+   achievement / frame element must vanish — across the whole app,
+   not just the dashboard. The rules below cover:
+     • dashboard widgets (.gam-bar, .lb-widget)
+     • profile tabs (achievements, shop, frames)
+     • textbook XP badges and progress cards (.hero-xp-badge, .po-xp,
+       .xp-bar, .xp-card)
+     • a catch-all [data-gamified] hook that wraps any future block —
+       authors of new pages should wrap XP UI in a <div data-gamified>
+       instead of inventing new classes. */
 body.no-gamification .gam-bar,
 body.no-gamification .lb-widget,
 body.no-gamification .achievements-section,
 body.no-gamification #tab-btn-achievements,
 body.no-gamification #tab-btn-shop,
 body.no-gamification #tab-achievements,
-body.no-gamification #tab-shop { display: none !important; }
+body.no-gamification #tab-shop,
+body.no-gamification #frames-section,
+body.no-gamification .hero-xp-badge,
+body.no-gamification .po-xp,
+body.no-gamification .xp-card,
+body.no-gamification .xp-bar,
+body.no-gamification .xp-pill,
+body.no-gamification .xp-badge,
+body.no-gamification [data-gamified] { display: none !important; }
 
 /* ══════════════════════════════════════════
    RESPONSIVE — SMALL PHONES (≤ 480px)