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/Referral.tsx

@@ -3,6 +3,7 @@ import { useNavigate } from 'react-router';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { referralApi } from '../api/referral';
+import { usePlatform } from '../platform';
 import { copyToClipboard } from '../utils/clipboard';
 import { brandingApi } from '../api/branding';
 import { partnerApi } from '../api/partners';
@@ -226,6 +227,8 @@ export default function Referral() {
     }
   };
 
+  const { openTelegramLink } = usePlatform();
+
   const shareLink = () => {
     if (!referralLink) return;
     const shareText = t('referral.shareMessage', {
@@ -247,7 +250,7 @@ export default function Referral() {
     const telegramUrl = `https://t.me/share/url?url=${encodeURIComponent(
       referralLink,
     )}&text=${encodeURIComponent(shareText)}`;
-    window.open(telegramUrl, '_blank', 'noopener,noreferrer');
+    openTelegramLink(telegramUrl);
   };
 
   if (isLoading) {