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/AskScreen.tsx

@@ -12,6 +12,7 @@ import { Diagram } from '@/diagram';
 import { MathText } from '@/lib/MathText';
 import { friendlyError } from '@/lib/errors';
 import { toFa } from '@/lib/format';
+import { useGateHold } from '@/lib/useAsync';
 
 const STARTERS = ['این فصل درباره‌ی چیه؟', 'یه مثالِ ساده برام حل کن', 'چطور برای امتحان تمرین کنم؟'];
 
@@ -23,9 +24,16 @@ export function AskScreen({ lessonId, questionId, prompt }: { lessonId?: number;
   const [busy, setBusy] = useState(false);
   // «X سوالِ رایگانِ امروز + Y سوالِ خریده‌شده»؛ پیش از اولین سوال از سرور، بعد از هر جواب از خودِ جواب.
   const [quota, setQuota] = useState<{ free: number; credits: number } | null>(null);
+  const [quotaDone, setQuotaDone] = useState(false);
   useEffect(() => {
-    api.ai.quota().then((q) => setQuota({ free: q.remainingQuota, credits: q.credits })).catch(() => {});
+    api.ai
+      .quota()
+      .then((q) => setQuota({ free: q.remainingQuota, credits: q.credits }))
+      .catch((err: unknown) => console.warn('ai quota lookup failed', err))
+      .finally(() => setQuotaDone(true));
   }, []);
+  // صفحه وقتی می‌آید که تاریخچه و سهمیه رسیده باشند؛ وگرنه اول خوش‌آمد و بعد پیام‌های قبلی رویش می‌پرید.
+  useGateHold(!chat.historyLoaded || !quotaDone);
   const listEnd = useRef<HTMLDivElement>(null);
   const autoSent = useRef(false);