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/styles/index.css

@@ -119,3 +119,7 @@
 .spark { animation: spark 2.4s ease-in-out infinite; transform-box: fill-box; transform-origin: center; }
 @keyframes rise { 0% { transform: translateY(16px); opacity: 0; } 15%, 85% { opacity: .55; } 100% { transform: translateY(-110px); opacity: 0; } }
 .rise { animation: rise 7s linear infinite; will-change: transform, opacity; }
+
+/* نوارِ انتظارِ میانِ دو صفحه (MainApp → HoldBar). */
+@keyframes hold-bar { 0% { transform: translateX(120%); } 100% { transform: translateX(-320%); } }
+.hold-bar { animation: hold-bar 0.9s cubic-bezier(.4,0,.2,1) infinite; will-change: transform; }