feat(a11y): cross-platform hardening + modal focus-trap from impeccable audit

Responsive / viewport:
- add .min-h-viewport / .h-viewport utilities (100dvh + Telegram --tg-viewport-stable-height)
- migrate min-h-screen / h-screen / 100vh across 18 files
- reveal hover-only controls on focus-within + touch (desktop nav, admin settings)
- grid breakpoints (TopUpAmount, Contests), larger touch targets, nav aria-labels

Platform routing (Telegram WebView correctness):
- clipboard -> copyToClipboard util with execCommand fallback (10 files)
- window.open -> openTelegramLink / openLink (Profile, Referral, ChannelSubscriptionScreen)
- window.confirm -> useNativeDialog (admin pages); PromoOffersSection -> useDestructiveConfirm
- window.prompt -> usePrompt / PromptDialogHost (TipTap link editors)
- ESLint no-restricted-properties guard against regressions (adapters/clipboard util exempt)

Modal accessibility:
- new useFocusTrap hook (focus trap, Esc, scroll lock, focus restore)
- role=dialog / aria-modal / focus-trap: Polls, SuccessNotificationModal, AdminPolicies,
  AdminPromoGroups, AdminCampaigns, BroadcastPreview (Telegram + Email)
- new global usePrompt store + PromptDialogHost

src/pages/Subscription.tsx

@@ -12,6 +12,7 @@ import { HoverBorderGradient } from '../components/ui/hover-border-gradient';
 import { useTrafficZone } from '../hooks/useTrafficZone';
 import { formatTraffic } from '../utils/formatTraffic';
 import { getGlassColors } from '../utils/glassTheme';
+import { copyToClipboard } from '../utils/clipboard';
 import { useTheme } from '../hooks/useTheme';
 import InsufficientBalancePrompt from '../components/InsufficientBalancePrompt';
 import { useCurrency } from '../hooks/useCurrency';
@@ -554,7 +555,7 @@ export default function Subscription() {
 
   const copyUrl = () => {
     if (displayedConnectionUrl) {
-      navigator.clipboard.writeText(displayedConnectionUrl);
+      void copyToClipboard(displayedConnectionUrl);
       setCopied(true);
       setTimeout(() => setCopied(false), 2000);
     }