navie_rag_agent实现冗余

在navie_rag_agent中，generate节点的逻辑

<img width="1255" height="721" alt="Image" src="https://github.com/user-attachments/assets/85b73203-3e5a-4102-b20f-09458c070213" />
与retrieve功能实现重复

<img width="1212" height="807" alt="Image" src="https://github.com/user-attachments/assets/e602bc6b-16d2-4f76-8da1-2d90537f8cc2" />