BUG: Always defaults to openrouter Gemini

[GratefulDave]

I have both a GEMINI_API_KEY and OPENROUTER_API_KEY. Model defaults only to openrouter options with no option for direct google gemini api key usage.

[thdxr]

env key we respect for google is https://github.com/sst/models.dev/blob/dev/providers/google/provider.toml#L2