Fixed the web UI bug where the chat window kept showing gemini-3.1-pro-preview even after picking a different model. The selected model now updates the agent state directly, so the chat button and the runtime stay in sync.
What Changed
- State Sync: Selecting a model now writes the chosen model back into the active agent state instead of leaving the old Gemini placeholder in place.
- Immediate Rerender: The model button in the chat window refreshes as soon as a new model is chosen.
- Browser Path: The local browser model is now represented as a real model object, so the UI can display it explicitly instead of pretending everything is Gemini.
This fixes the mismatch between the picker and the chat header, which made it look like model changes were being ignored.