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

backend/app/core/config.py

@@ -25,6 +25,9 @@ class Settings(BaseSettings):
         "NEWS_PLATFORM_BASE_URL", "http://192.168.1.200:63120"
     )
 
+    # 数字分身 SQLite 数据库路径（直连数字分身应用的 SQLite）
+    AVATAR_DB_PATH: str = os.getenv("AVATAR_DB_PATH", "")
+
     # 日志目录
     LOG_DIR: str = "/app/logs"