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/TopUpAmount.tsx

@@ -13,6 +13,7 @@ import { staggerContainer, staggerItem } from '@/components/motion/transitions';
 import type { PaymentMethod, PaymentMethodOption } from '../types';
 import BentoCard from '../components/ui/BentoCard';
 import { saveTopUpPendingInfo } from '../utils/topUpStorage';
+import { copyToClipboard } from '@/utils/clipboard';
 
 // Icons
 const StarIcon = () => (
@@ -400,7 +401,7 @@ export default function TopUpAmount() {
   const handleCopyUrl = async () => {
     if (!paymentUrl) return;
     try {
-      await navigator.clipboard.writeText(paymentUrl);
+      await copyToClipboard(paymentUrl);
       setCopied(true);
       setTimeout(() => setCopied(false), 2000);
     } catch {
@@ -522,7 +523,7 @@ export default function TopUpAmount() {
 
       {/* Quick amount buttons */}
       {quickAmounts.length > 0 && (
-        <motion.div variants={staggerItem} className="grid grid-cols-4 gap-2">
+        <motion.div variants={staggerItem} className="grid grid-cols-2 gap-2 sm:grid-cols-4">
           {quickAmounts.map((a) => {
             const val = getQuickValue(a);
             const isSelected = amount === val;