Subscription store, paywall on locked units, profile subscription bar, Tadrisino branding

- Store opens with two choices (subscription / question packs); 3- and 6-month cards
  show per-month price and saving.
- Units that need a subscription show a crown badge and open the store; a 402 from
  the quiz goes there too. «ادامه بده» skips locked units.
- Profile: subscription card with an animated days-left bar (planDurationDays).
- BrandMark (SVG) on splash, home header and footer; copyright footer; floating math
  glyphs on splash. CSS transform/opacity only; honours reduced motion.

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

src/components/BrandFooter.tsx

@@ -0,0 +1,13 @@
+import { toFa } from '@/lib/format';
+import { BrandMark } from '@/components/BrandMark';
+
+/** امضای تدریسینو پایینِ صفحه‌ها: نشان، نام و حقِ نشر، کوچک و کم‌رنگ. */
+export function BrandFooter() {
+  return (
+    <footer className="flex flex-col items-center gap-1 pb-4 pt-3 text-center">
+      <BrandMark size={24} tone="dark" />
+      <span className="text-[10px] text-muted">ریاضی، قدم‌به‌قدم، از روی کتابِ درسی</span>
+      <span className="text-[10px] text-faint">© {toFa(1405)} تدریسینو · همه‌ی حقوق محفوظ است</span>
+    </footer>
+  );
+}