feat: add Yolo-Auto provider

[harryvgiunta]

Adds Yolo-Auto (yolo-auto) to the built-in catalog as an OpenAI-compatible
chat-completions endpoint: https://yolo-auto.com/v1 with a key from
YOLO_AUTO_API_KEY.

Models are the stable aliases yolo and yolo-small. The models available to a
key are listed at GET https://yolo-auto.com/v1/models, and any of them can be
added locally through a ~/.tau/catalog.toml overlay.

Docs: https://yolo-auto.com/docs . Keys are free to create.