feat: admin back-office system + AI assistant with action commands

- Admin analytics (recharts charts, overview stats, trend analysis, time range selector)
- Admin permissions (AdminRole/AdminUser models, role CRUD, permission catalog)
- Admin system config (site/AI/member category tabs, per-key save)
- Admin operations (Banner CRUD, push notification send/delete)
- Admin user management (table, search, create/edit, ban/delete)
- Admin layout (custom top bar with branding + sidebar, admin AI assistant)
- Admin login (adminToken localStorage, adminInfo display)
- Admin AI assistant (purple '运营助手', context-aware prompts, action commands)
- Public AI assistant Phase B (action commands: navigate, setModel, startChat, openSkill, setParameter)
- Assistant context mapping + action executor
- Skills API fix: tags parsing fallback (JSON.parse → split)
- Sandbox crash fix: curScene fallback system prompt
- JWT token expiration: access 2h→7d, refresh 7d→30d, admin 8h→7d
- i18n: assistant-related translations (zh/en)
- PM2 ecosystem config for process management
- AI assistant login prompt fix: admin uses getAdminToken(), public uses apiFetch with token refresh

frontend/src/app/admin/login/page.tsx

@@ -29,6 +29,7 @@ export default function AdminLoginPage() {
       const data = await res.json();
       if (!res.ok) throw new Error(data.message || '管理员登录失败');
       localStorage.setItem('adminToken', data.token);
+      localStorage.setItem('adminInfo', JSON.stringify({ username: data.username, role: data.role }));
       toast.success('管理员登录成功');
       router.push('/admin');
     } catch (err: any) {