Update OpenAI error handling

[barryvdh]

This tries to parse the OpenAI error, so instead of a 400 invalid request, you get the actual errors.

[barryvdh]

Note, I've tested this with a few errors that came around, so not 100% if all errors are the same.

For example, uploading a .txt file would first give:

  Sending to model (gpt-5-mini) failed: HTTP request returned status code 400

but now:

  OpenAI Error: [invalid_request_error] The file type you uploaded is not supported. Please try again with a pdf (param: input, code: unsupported_file)

[sixlive]

Thanks!!