Add OpenAI-Compatible API Support

[toslali-ibm]

It would be great to support any OpenAI-compatible API as a backend.

• This would let users plug in alternative model providers such as ChatGPT, Ollama, or any custom deployment that follows the OpenAI API spec.
• Users should also be able to switch the LLM used for chat, rather than being restricted to Llama.

Reference: https://docs.ollama.com/api/openai-compatibility

[michaelbrinkworth]

@toslali-ibm
AI Badgr is OpenAI-compatible (same SDK + request/response shape).

If you want another optional provider, it should work via a base_url + API key swap — no refactor needed.

Happy to help verify with a real request if useful.