Fix image_url parameter to match recent OpenAI Docs

[kovrichard]

According to the recent OpenAI docs, image_url must be passed the following way to vision models:

{
  "type": "image_url",
  "image_url": {
    "url": f"data:image/jpeg;base64,{base64_image}"
  }
}

See here: https://platform.openai.com/docs/guides/vision/uploading-base-64-encoded-images

I also changed the Claude API route to avoid breaking existing vision models.

I have no access to Gemini Pro Vision, so that is the only vision model I could not test.