feat: add digital avatar management to admin dashboard

- Add avatars list page with pagination, search, status filter
- Add avatar detail dialog showing full info and config params
- Add on/off switch (active/inactive status toggle)
- Backend: avatar_service.py connects to digital avatar SQLite
- Backend: /api/avatars endpoints for list, detail, status update
- Sidebar menu item added below dashboard
- docker-compose: mount SQLite db and set AVATAR_DB_PATH env var

frontend/src/router/index.js

@@ -7,6 +7,7 @@ const routes = [
     children: [
       { path: '', redirect: '/dashboard' },
       { path: 'dashboard', component: () => import('@/views/Dashboard.vue'), meta: { title: '数据看板' } },
+      { path: 'avatars', component: () => import('@/views/Avatars.vue'), meta: { title: '数字分身管理' } },
       { path: 'users', component: () => import('@/views/Users.vue'), meta: { title: '虚拟用户管理' } },
       { path: 'interactions', component: () => import('@/views/Interactions.vue'), meta: { title: '互动记录' } },
       { path: 'ai-models', component: () => import('@/views/AIModels.vue'), meta: { title: 'AI模型配置' } },