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

docker-compose.yml

@@ -18,10 +18,12 @@ services:
       - SECRET_KEY=your-secret-key-change-in-production
       - AES_KEY=your-aes-key-32-chars-change-now!
       - TZ=Asia/Shanghai
+      - AVATAR_DB_PATH=/app/avatar.db
     volumes:
       - ./backend/app:/app/app    # ← 核心：代码目录直接挂载，改文件无需重建
       - ./backend/logs:/app/logs
       - ./backend/config:/app/config
+      - ./digital-avatar-app/backend/avatar.db:/app/avatar.db:ro   # 数字分身 SQLite（只读）
     depends_on:
       - ai-virtual-mysql
       - ai-virtual-redis