feat: Phase 4 — Admin panel (dashboard, users, moderation)

AdminPanel2 component with sidebar navigation:
- Dashboard: KPI cards (users, patches, premium, flagged)
- Users: search, filter by role, table with role dropdown to
  change user/premium/admin/banned per user
- Workshop moderation: filter flagged/deleted, approve/delete/restore
  actions per patch with status badges

Features:
- Role-protected: non-admins see 🔒 locked screen
- Sidebar nav: Dashboard / Usuarios / Workshop / Volver
- Admin button visible in Workshop nav for admin users
- Responsive: sidebar becomes horizontal tabs on mobile,
  KPIs 2x2 grid, table rows wrap

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/client/src/main.jsx

@@ -3,24 +3,27 @@ import { createRoot } from 'react-dom/client';
 import App from './App';
 import GameApp from './game/GameApp.jsx';
 import Workshop from './components/Workshop.jsx';
+import AdminPanel2 from './components/AdminPanel2.jsx';
 import { AuthProvider } from './services/AuthContext.jsx';
 import AuthModal from './components/AuthModal.jsx';
 import './index.css';
 
 function Root() {
-  const [mode, setMode] = useState('game'); // 'game' | 'sandbox' | 'workshop'
+  const [mode, setMode] = useState('game'); // 'game' | 'sandbox' | 'workshop' | 'admin'
 
   const nav = {
     toGame: () => setMode('game'),
     toSandbox: () => setMode('sandbox'),
     toWorkshop: () => setMode('workshop'),
+    toAdmin: () => setMode('admin'),
   };
 
   return (
     <AuthProvider>
       {mode === 'sandbox' && <App onSwitchToGame={nav.toGame} onSwitchToWorkshop={nav.toWorkshop} />}
       {mode === 'game' && <GameApp onSwitchToSandbox={nav.toSandbox} onSwitchToWorkshop={nav.toWorkshop} />}
-      {mode === 'workshop' && <Workshop onSwitchToSandbox={nav.toSandbox} onSwitchToGame={nav.toGame} />}
+      {mode === 'workshop' && <Workshop onSwitchToSandbox={nav.toSandbox} onSwitchToGame={nav.toGame} onSwitchToAdmin={nav.toAdmin} />}
+      {mode === 'admin' && <AdminPanel2 onBack={nav.toGame} />}
       <AuthModal />
     </AuthProvider>
   );