Two bugs prevented pinned models from appearing in the chat model picker:
1. _fetch_models() only used _cached_model_ids(), ignoring pinned_models.
Since Fireworks AI doesn't list kimi-k2p6-turbo in /v1/models, the
cached list was empty, so the endpoint showed as offline with no models.
2. _curate_models() filtered unknown pinned IDs into models_extra, but the
chat UI only reads models (primary list). Pinned models stayed invisible.
Fix: use _visible_models() to merge cached + pinned, then promote pinned
IDs from models_extra to models so they appear in the dropdown.
Closes#1521 follow-up
20cc23c9bd