bug: error state if small_model is set to unenabled provider #1643

If I set this in my opencode.jsonc:

{
  ...,
 "model": "anthropic/claude-sonnet-4-20250514",
}

And I am not signed into anthropic, opencode will handle it properly and default to a model I do have access to

However, if I set:

{
  ...,
 "small_model": "anthropic/claude-3-5-haiku-20241022",
}

And I am not signed into anthropic, opencode will hang and error out at the title generation step

I think we should gracefully handle it but emit a warning or something