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/admin/ButtonsTab.tsx

@@ -11,6 +11,7 @@ import {
 } from '../../api/buttonStyles';
 import { Toggle } from './Toggle';
 import { useNotify } from '../../platform/hooks/useNotify';
+import { useNativeDialog } from '../../platform/hooks/useNativeDialog';
 
 type StyleValue = 'primary' | 'success' | 'danger' | 'default';
 
@@ -42,6 +43,7 @@ export function ButtonsTab() {
   const { t } = useTranslation();
   const queryClient = useQueryClient();
   const notify = useNotify();
+  const { confirm: confirmDialog } = useNativeDialog();
 
   const { data: serverStyles } = useQuery({
     queryKey: ['button-styles'],
@@ -341,8 +343,8 @@ export function ButtonsTab() {
       {/* Reset */}
       <div className="flex justify-end">
         <button
-          onClick={() => {
-            if (window.confirm(t('admin.buttons.resetConfirm'))) {
+          onClick={async () => {
+            if (await confirmDialog(t('admin.buttons.resetConfirm'))) {
               resetMutation.mutate();
             }
           }}