Smooth screen transitions: new screen waits hidden until its data arrives, no half-built flash

- Navigator stage: the next screen mounts hidden under the current one and is revealed only when its
  first data has arrived (ScreenGate held by useAsync/useGateHold), at most 450 ms; a thin top bar shows
  after 120 ms of waiting. Push slides from the left, back from the right, tabs only fade.
- Session cache (stale-while-revalidate) for screen GETs: revisited screens draw instantly.
- Home map and stats are fetched during the splash, so the first screen arrives complete.
- Entrance pop-ins (mascot, islands, lesson cards) run on first view only, not on every revisit.
- Shop status card shows placeholders instead of a wrong «نداری» while loading.
- Re-tapping the open tab scrolls to top instead of reloading; sheets close with a swipe down.
- Quiz: «۱ از ۴» instead of «۱/۴» (read as a fraction), varied praise, «N تا پشتِ هم درست»,
  growth-mindset copy after a weak round, zero-reward tiles hidden.
- Streak: a concrete next step when the streak is 0 or today is still empty.

Checked in headless Chrome against the local backend (frame captures at 150 ms and 700 ms latency,
rapid tab tapping, full quiz run). Not checked on a real phone or iOS Safari.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/screens/LessonsScreen.tsx

@@ -11,6 +11,7 @@ import { EmptyState, ErrorState, LoadingState, ProgressBar, Screen, ScreenHeader
 import { iconFor } from '@/components/NodeIcon';
 import { toFa } from '@/lib/format';
 import { MathText } from '@/lib/MathText';
+import { useFirstVisit } from '@/lib/firstVisit';
 
 /**
  * تبِ «درس‌ها»: فصل ← جزیره ← درس. فصل‌ها اول بسته‌اند و بالای صفحه یک کارتِ «ادامه بده» هست.
@@ -117,9 +118,10 @@ function UnitCard({
   const Icon = iconFor(unit.nodes[0]?.icon, index);
   const nav = useNav();
   const premium = unit.requiresSubscription;
+  const intro = useFirstVisit(`unit-card:${unit.id}`);
   return (
     <motion.div
-      initial={{ opacity: 0, y: 12 }}
+      initial={intro ? { opacity: 0, y: 12 } : { opacity: 1, y: 0 }}
       animate={{ opacity: 1, y: 0 }}
       transition={{ delay: Math.min(index, 8) * 0.04 }}
       className="overflow-hidden rounded-2xl bg-white"