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/SettingsTableRow.tsx

@@ -142,7 +142,7 @@ export function SettingsTableRow({
             <button
               onClick={onReset}
               disabled={isResetting}
-              className="flex-shrink-0 rounded-lg p-1.5 text-dark-500 opacity-0 transition-all hover:bg-dark-700 hover:text-dark-200 disabled:opacity-50 group-hover:opacity-100 max-lg:opacity-100"
+              className="flex-shrink-0 rounded-lg p-1.5 text-dark-500 opacity-0 transition-all hover:bg-dark-700 hover:text-dark-200 disabled:opacity-50 group-focus-within:opacity-100 group-hover:opacity-100 max-lg:opacity-100 [@media(hover:none)]:opacity-100"
               title={t('admin.settings.reset')}
               aria-label={t('admin.settings.reset')}
             >
@@ -157,7 +157,7 @@ export function SettingsTableRow({
               'flex-shrink-0 rounded-lg p-1.5 transition-all',
               isFavorite
                 ? 'text-warning-400 hover:bg-warning-500/15'
-                : 'text-dark-500 opacity-0 hover:bg-dark-700/50 hover:text-warning-400 group-hover:opacity-100 max-lg:opacity-100',
+                : 'text-dark-500 opacity-0 hover:bg-dark-700/50 hover:text-warning-400 group-focus-within:opacity-100 group-hover:opacity-100 max-lg:opacity-100 [@media(hover:none)]:opacity-100',
             )}
             title={
               isFavorite