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

ecosystem.config.js

@@ -0,0 +1,27 @@
+module.exports = {
+  apps: [
+    {
+      name: 'backend',
+      cwd: '/home/wlt/ai-learning-platform/backend',
+      script: 'node',
+      args: 'dist/main.js',
+      instances: 1,
+      autorestart: true,
+      watch: false,
+      max_restarts: 10,
+      env: {
+        NODE_ENV: 'development'
+      }
+    },
+    {
+      name: 'frontend',
+      cwd: '/home/wlt/ai-learning-platform/frontend',
+      script: 'npm',
+      args: 'run dev',
+      instances: 1,
+      autorestart: true,
+      watch: false,
+      max_restarts: 10
+    }
+  ]
+}