Complete back button logic for all admin pages in Telegram Mini App

Main sections navigate to /admin (15 pages)
Detail/edit pages navigate to parent lists (16 pages)
All pages use useBackButton hook with proper navigation paths
Native Telegram back button in Mini App, UI button on web
Email template pages keep UI-only back buttons as required

src/pages/AdminCampaignStats.tsx

@@ -4,6 +4,7 @@ import { useQuery } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { campaignsApi, CampaignBonusType } from '../api/campaigns';
 import { AdminBackButton } from '../components/admin';
+import { useBackButton } from '../platform/hooks/useBackButton';
 
 // Icons
 const CopyIcon = () => (
@@ -97,6 +98,8 @@ export default function AdminCampaignStats() {
   const [copied, setCopied] = useState(false);
   const [showUsers, setShowUsers] = useState(false);
 
+  useBackButton(() => navigate('/admin/campaigns'));
+
   // Fetch stats
   const {
     data: stats,