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/components/connection/blocks/BlockButtons.tsx

@@ -1,6 +1,7 @@
 import { useState, useCallback } from 'react';
 import { useTranslation } from 'react-i18next';
 import type { RemnawaveButtonClient, LocalizedText } from '@/types';
+import { copyToClipboard } from '@/utils/clipboard';
 
 // eslint-disable-next-line no-script-url
 const dangerousSchemes = ['javascript:', 'data:', 'vbscript:', 'file:'];
@@ -64,16 +65,7 @@ export function BlockButtons({
   const [copied, setCopied] = useState(false);
 
   const handleCopy = useCallback(async (url: string) => {
-    try {
-      await navigator.clipboard.writeText(url);
-    } catch {
-      const textarea = document.createElement('textarea');
-      textarea.value = url;
-      document.body.appendChild(textarea);
-      textarea.select();
-      document.execCommand('copy');
-      document.body.removeChild(textarea);
-    }
+    await copyToClipboard(url);
     setCopied(true);
     setTimeout(() => setCopied(false), 2000);
   }, []);