feature: support external Ollama via native Ollama API

[sammcj]

It would be great if you could provide the URL or container name for an existing Ollama server and have Helix use it's native API (rather than the openai compatible API).

The native API offers quite a lot more than the openai compatible API which should really only be used as a last resort for incompatible apps.

[rusenask]

hi @sammcj, thanks for checking out Helix! What in particular do you have in mind about ollama's chat api that is not supported in the openai API?