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/Wheel.tsx

@@ -368,6 +368,10 @@ export default function Wheel() {
     setIsPayingStars(true);
     // In browser: pre-open window synchronously (direct user gesture) to avoid popup blocker
     if (!capabilities.hasInvoice) {
+      // Web-only: synchronously pre-open a tab during the user gesture to dodge the
+      // popup blocker before the async invoice URL resolves. Not reached in Telegram
+      // (hasInvoice is true there, so the native invoice flow is used instead).
+      // eslint-disable-next-line no-restricted-properties
       preOpenedWindowRef.current = window.open('about:blank', '_blank') || null;
     }
     starsInvoiceMutation.mutate();