bug：gpt-5.6系列的fast模式在 apikey和oauth方式下模型单价不统一

输入、输出模型价格不统一

apiKey接入上游的是这样

<img width="332" height="232" alt="Image" src="https://github.com/user-attachments/assets/2e3cc72c-bfc0-4663-9811-e524cfb1ba92" />

oauth上游是这样

<img width="404" height="280" alt="Image" src="https://github.com/user-attachments/assets/064bdcc6-ffc2-4f72-a4ff-cfeadf16ac1b" />