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/blocking/ChannelSubscriptionScreen.tsx

@@ -2,21 +2,10 @@ import { useState, useEffect, useCallback, useRef } from 'react';
 import { useTranslation } from 'react-i18next';
 import { useBlockingStore } from '../../store/blocking';
 import { apiClient, isChannelSubscriptionError } from '../../api/client';
+import { usePlatform } from '../../platform';
 
 const CHECK_COOLDOWN_SECONDS = 5;
 
-function safeOpenUrl(url: string | undefined | null): void {
-  if (!url) return;
-  try {
-    const parsed = new URL(url);
-    if (parsed.protocol === 'https:' || parsed.protocol === 'http:') {
-      window.open(url, '_blank', 'noopener');
-    }
-  } catch {
-    // invalid URL, do nothing
-  }
-}
-
 export default function ChannelSubscriptionScreen() {
   const { t } = useTranslation();
   const channelInfo = useBlockingStore((state) => state.channelInfo);
@@ -25,6 +14,28 @@ export default function ChannelSubscriptionScreen() {
   const [cooldown, setCooldown] = useState(0);
   const [error, setError] = useState<string | null>(null);
   const isCheckingRef = useRef(false);
+  const { openLink, openTelegramLink } = usePlatform();
+
+  // Route channel links through the platform adapter: inside the Telegram
+  // WebView a raw window.open is intercepted by the client and the link
+  // silently fails to open. t.me links use openTelegramLink; others openLink.
+  const openChannel = useCallback(
+    (url: string | undefined | null) => {
+      if (!url) return;
+      try {
+        const parsed = new URL(url);
+        if (parsed.protocol !== 'https:' && parsed.protocol !== 'http:') return;
+        if (parsed.hostname === 't.me' || parsed.hostname.endsWith('.t.me')) {
+          openTelegramLink(url);
+        } else {
+          openLink(url);
+        }
+      } catch {
+        // invalid URL, do nothing
+      }
+    },
+    [openLink, openTelegramLink],
+  );
 
   // Cooldown timer
   useEffect(() => {
@@ -100,7 +111,7 @@ export default function ChannelSubscriptionScreen() {
                 <span className="text-sm font-medium text-white">{ch.title || ch.channel_id}</span>
                 {ch.channel_link && (
                   <button
-                    onClick={() => safeOpenUrl(ch.channel_link)}
+                    onClick={() => openChannel(ch.channel_link)}
                     className="rounded-lg bg-blue-500/20 px-3 py-1 text-xs font-medium text-blue-400 hover:bg-blue-500/30"
                   >
                     {t('blocking.channel.openChannel')}
@@ -114,7 +125,7 @@ export default function ChannelSubscriptionScreen() {
         {/* Fallback: single channel (legacy) */}
         {channels.length === 0 && channelInfo?.channel_link && (
           <button
-            onClick={() => safeOpenUrl(channelInfo.channel_link)}
+            onClick={() => openChannel(channelInfo.channel_link)}
             className="mb-6 flex w-full items-center justify-center gap-3 rounded-xl bg-gradient-to-r from-blue-500 to-cyan-500 px-6 py-4 font-semibold text-white transition-all duration-200 hover:from-blue-600 hover:to-cyan-600"
           >
             {t('blocking.channel.openChannel')}