- Custom endpoints can serve any model, so skip validation for
provider='custom' in validate_requested_model(). Previously it
would reject any model name since there's no static catalog or
live API to check against.
- Show clear setup instructions when switching to custom endpoint
without OPENAI_BASE_URL/OPENAI_API_KEY configured.
- Added curated model lists for Nous Portal and OpenAI Codex to
_PROVIDER_MODELS so /model shows their available models.