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/api/__init__.py

@@ -1,6 +1,6 @@
 """API路由汇总"""
 from fastapi import APIRouter
-from app.api.endpoints import users, interactions, ai_models, dashboard, system, logs
+from app.api.endpoints import users, interactions, ai_models, dashboard, system, logs, avatars
 
 router = APIRouter()
 
@@ -10,3 +10,4 @@ router.include_router(ai_models.router, prefix="/ai-models", tags=["AI模型配
 router.include_router(dashboard.router, prefix="/dashboard", tags=["数据看板"])
 router.include_router(system.router, prefix="/system", tags=["系统设置"])
 router.include_router(logs.router, prefix="/logs", tags=["日志管理"])
+router.include_router(avatars.router, prefix="/avatars", tags=["数字分身管理"])