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/app/MainApp.tsx

@@ -110,7 +110,7 @@ function RouteView({ route, onSignedOut }: { route: Route } & Pick<Props, 'onSig
     case 'home': return <HomeScreen />;
     case 'lessons': return <LessonsScreen />;
     case 'ask': return <AskScreen lessonId={route.lessonId} questionId={route.questionId} prompt={route.prompt} />;
-    case 'subscription': return <SubscriptionScreen />;
+    case 'subscription': return <SubscriptionScreen key={route.view ?? ''} initialView={route.view} />;
     case 'profile': return <ProfileScreen onSignedOut={onSignedOut} />;
     case 'unit': return <UnitScreen unitId={route.unitId} />;
     case 'lesson': return <LessonScreen lessonId={route.lessonId} nodeId={route.nodeId} />;