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/PromptDialogHost.tsx

@@ -0,0 +1,72 @@
+import { useEffect, useState, type FormEvent } from 'react';
+import { createPortal } from 'react-dom';
+import { useTranslation } from 'react-i18next';
+import { useFocusTrap } from '../hooks/useFocusTrap';
+import { usePromptStore } from '../store/promptDialog';
+
+/**
+ * Global host for usePrompt(). Mount once near the app root.
+ * Renders an accessible text-input dialog (focus-trapped, Esc/Enter, scroll-locked)
+ * as a cross-platform replacement for window.prompt, which the Telegram WebView ignores.
+ */
+export function PromptDialogHost() {
+  const request = usePromptStore((s) => s.request);
+  const submit = usePromptStore((s) => s.submit);
+  const cancel = usePromptStore((s) => s.cancel);
+  const { t } = useTranslation();
+  const [value, setValue] = useState('');
+
+  const open = request !== null;
+  const dialogRef = useFocusTrap<HTMLFormElement>(open, { onEscape: cancel });
+
+  useEffect(() => {
+    if (request) setValue(request.initialValue ?? '');
+  }, [request]);
+
+  if (!request) return null;
+
+  const handleSubmit = (e: FormEvent) => {
+    e.preventDefault();
+    const trimmed = value.trim();
+    if (!trimmed) {
+      cancel();
+      return;
+    }
+    submit(trimmed);
+  };
+
+  return createPortal(
+    <div className="fixed inset-0 z-[120] flex items-center justify-center p-4">
+      <div className="absolute inset-0 bg-black/60" onClick={cancel} aria-hidden="true" />
+      <form
+        ref={dialogRef}
+        role="dialog"
+        aria-modal="true"
+        aria-label={request.title ?? request.label}
+        onSubmit={handleSubmit}
+        className="card relative w-full max-w-sm space-y-4"
+      >
+        {request.title && <h2 className="text-lg font-semibold text-dark-50">{request.title}</h2>}
+        <label className="block">
+          <span className="label">{request.label}</span>
+          <input
+            type={request.inputType ?? 'text'}
+            value={value}
+            onChange={(e) => setValue(e.target.value)}
+            placeholder={request.placeholder}
+            className="input"
+          />
+        </label>
+        <div className="flex justify-end gap-2">
+          <button type="button" onClick={cancel} className="btn-secondary">
+            {request.cancelLabel ?? t('common.cancel')}
+          </button>
+          <button type="submit" className="btn-primary">
+            {request.submitLabel ?? t('common.ok', 'OK')}
+          </button>
+        </div>
+      </form>
+    </div>,
+    document.body,
+  );
+}