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/AdminChannelSubscriptions.tsx

@@ -2,6 +2,7 @@ import { useState } from 'react';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { useHaptic, useNotify } from '../platform';
+import { useNativeDialog } from '../platform/hooks/useNativeDialog';
 import {
   adminChannelsApi,
   type RequiredChannel,
@@ -656,8 +657,10 @@ export default function AdminChannelSubscriptions() {
     toggleMutation.mutate(id);
   };
 
-  const handleDelete = (id: number) => {
-    if (window.confirm(t('admin.channelSubscriptions.deleteConfirm'))) {
+  const { confirm: confirmDialog } = useNativeDialog();
+
+  const handleDelete = async (id: number) => {
+    if (await confirmDialog(t('admin.channelSubscriptions.deleteConfirm'))) {
       deleteMutation.mutate(id);
     }
   };