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/Contests.tsx

@@ -137,7 +137,7 @@ export default function Contests() {
 
                 {/* Render game based on type */}
                 {(gameData.game_type === 'quest' || gameData.game_type === 'locks') && (
-                  <div className="grid grid-cols-5 gap-2">
+                  <div className="grid grid-cols-3 gap-2 sm:grid-cols-5">
                     {Array.from({
                       length: gameData.game_data.total || gameData.game_data.grid_size || 9,
                     }).map((_, i) => (
@@ -154,7 +154,7 @@ export default function Contests() {
                 )}
 
                 {gameData.game_type === 'server' && (
-                  <div className="grid grid-cols-5 gap-2">
+                  <div className="grid grid-cols-3 gap-2 sm:grid-cols-5">
                     {gameData.game_data.flags?.map((flag: string, i: number) => (
                       <button
                         key={i}