Check for AI token authentication

[RobertIsmo]

add a check to the cli to see if the the tokens in the .env are valid.

[RobertIsmo]

I am going to reach out to claude code, gemini cli, openai codex, to get a clean auth check added, of course you can just try and run something and see if it fails, but that is super hacky. Will probably send contributions their way and reference them here for progress.

[RobertIsmo]

Overall apart of the whole improved DX from #26 added to this should also be model access checks as well, but I doubt that will be merged in as cleanly upstream.