Cannot see all models at /models, only GPT-4.1 available, and CAPIError 400 after model selection

**Description:**
- When accessing /models, I cannot see all available models—only GPT-4.1 is shown.
- Attempting to use other models results in:
CAPIError: 400 The requested model is not supported. (Request ID: 7F9A:4D9FC:86257D:B13592:69C908B5)
- After this error, Copilot’s behavior is not normal.

**Steps to Reproduce:**
1. Go to /models in Copilot.
2. Try to select a different model.
3. Observe the error and limited model list.

**Expected:**
All available models should be listed and selectable.

**Actual:**
Only GPT-4.1 is available, and selecting others causes errors.

Start by reproducing the issue from the /models entry point: check the available model list, select a model other than GPT-4.1, and capture the CAPIError 400 behavior. Done means all available models are listed, selectable, and do not leave Copilot in an abnormal state after selection.

由索引模型根据 Issue 内容生成。