[Feat] 请支持第三方NewAPI端点添加，现在报错Error: Failed to import registry: Invalid URL (GET /v1)

What feature would you like to see?

[Feat] 请支持第三方平台端点（例如NewAPI平台）的添加，现在按如下格式在/provider命令下手动添加 Provider会报错:

 Add provider
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     Known third-party provider
   ❯ Custom registry (api.json)

报错1如下：

http://192.168.2.197:3000/
Error: Failed to import registry: Unexpected token '<', "<!doctype "... is not valid JSON

报错2如下：

http://192.168.2.197:3000/v1
Error: Failed to import registry: Invalid URL (GET /v1)

希望能仅通过base url完成API端点的添加。

Additional information

N/A

Start with the /provider command flow and the code that imports a custom registry from the supplied endpoint. Reproduce the two reported cases using a base URL, then trace how the URL is validated and how registry responses are parsed. Done means a compatible third-party endpoint can be added using only its base URL without either reported error.