[Feature] Support for OpenAI responses endpoint

[itspolly]

Problem Description
No support for OpenAI responses endpoint which means you cannot use GPT-5 Pro in this app.

Proposed Solution

• Add support for the OpenAI responses endpoint so that GPT-5 Pro can be used in your app.

Additional Context

See https://platform.openai.com/docs/api-reference/responses for details.

---

问题描述
请描述您遇到的问题或难题，以及为什么这使得使用软件变得困难或令人沮丧。

解决思路
请提供一个清晰、简洁的描述，说明您希望看到的功能或解决方案。

附加上下文
请提供任何其他上下文或信息，以便更好地理解您的功能请求，例如截图、示例或用例。

[VincentHXZ]

I can't set the OpenAI API path to v1/responses, even with a custom provider — it must be v1/chat/completions.