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/Polls.tsx

@@ -2,6 +2,7 @@ import { useState } from 'react';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { pollsApi, PollInfo, PollQuestion } from '../api/polls';
+import { useFocusTrap } from '../hooks/useFocusTrap';
 
 const ClipboardIcon = () => (
   <svg className="h-6 w-6" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
@@ -107,6 +108,10 @@ export default function Polls() {
     setCompletionMessage(null);
   };
 
+  const pollDialogRef = useFocusTrap<HTMLDivElement>(!!selectedPoll, {
+    onEscape: handleClosePoll,
+  });
+
   if (isLoading) {
     return (
       <div className="flex min-h-64 items-center justify-center">
@@ -133,10 +138,28 @@ export default function Polls() {
       {/* Poll Modal */}
       {selectedPoll && (
         <div className="fixed inset-0 z-50 flex items-center justify-center p-4">
-          <div className="card max-h-[80vh] w-full max-w-lg overflow-y-auto">
+          <div
+            className="absolute inset-0 bg-black/60"
+            onClick={handleClosePoll}
+            aria-hidden="true"
+          />
+          <div
+            ref={pollDialogRef}
+            role="dialog"
+            aria-modal="true"
+            aria-labelledby="poll-dialog-title"
+            tabIndex={-1}
+            className="card relative max-h-[80vh] w-full max-w-lg overflow-y-auto"
+          >
             <div className="mb-4 flex items-center justify-between">
-              <h2 className="text-xl font-bold">{selectedPoll.title}</h2>
-              <button onClick={handleClosePoll} className="text-dark-400 hover:text-dark-200">
+              <h2 id="poll-dialog-title" className="text-xl font-bold">
+                {selectedPoll.title}
+              </h2>
+              <button
+                onClick={handleClosePoll}
+                aria-label={t('common.close')}
+                className="text-dark-400 hover:text-dark-200"
+              >
                 <svg className="h-6 w-6" fill="none" viewBox="0 0 24 24" stroke="currentColor">
                   <path
                     strokeLinecap="round"