feat: add success notification modal for balance and subscription events

- Add zustand store for global success notifications
- Create SuccessNotificationModal component with prominent UI
- Update WebSocketNotifications to show modal for important events:
  - balance.topup shows balance topped up modal
  - subscription.activated shows activation modal
  - subscription.renewed shows renewal modal
- Add translations for all locales (ru, en, zh, fa)

src/components/layout/Layout.tsx

@@ -7,6 +7,7 @@ import LanguageSwitcher from '../LanguageSwitcher';
 import PromoDiscountBadge from '../PromoDiscountBadge';
 import TicketNotificationBell from '../TicketNotificationBell';
 import WebSocketNotifications from '../WebSocketNotifications';
+import SuccessNotificationModal from '../SuccessNotificationModal';
 import AnimatedBackground from '../AnimatedBackground';
 import { contestsApi } from '../../api/contests';
 import { pollsApi } from '../../api/polls';
@@ -456,6 +457,9 @@ export default function Layout({ children }: LayoutProps) {
       {/* Global WebSocket notifications handler */}
       <WebSocketNotifications />
 
+      {/* Global success notification modal */}
+      <SuccessNotificationModal />
+
       {/* Animated Background */}
       <AnimatedBackground />