feat(admin): 实现动态路由菜单并修复rbac菜单树构建问题

- 修复rbac.py中菜单树构建逻辑，将`elif not menu.parentId`改为`else`，避免父菜单不存在时子菜单丢失
- 新增后端`/api/admin/system/routers`接口，作为动态路由菜单的API
- 前端新增`getRouters` API并整合到用户信息加载流程
- 添加菜单扁平化工具函数，更新路由注册逻辑以支持嵌套路由
- 新增相关测试用例并更新API和集成文档

WonderQ-Admin/app/routers/system.py

@@ -111,6 +111,17 @@ def profile(
     }
 
 
+@router.get("/routers")
+def routers(
+    user: AdminUser = Depends(require_admin),
+    db: Session = Depends(get_db),
+    store: AdminSessionStore = Depends(get_admin_session_store),
+):
+    """Return the authenticated user's visible menu tree for dynamic routing."""
+    context = build_admin_permission_context(user, db, store)
+    return {"code": 200, "msg": "success", "data": context["menus"]}
+
+
 @router.get("/users")
 def list_users(_user: AdminUser = Depends(require_permission("system:user:read")), db: Session = Depends(get_db)):
     users = list(db.scalars(select(AdminUser).order_by(AdminUser.createdAt.desc())).all())