The idle guard prevented the keybinding from working while the agent was
generating, even though the profile selector button in the UI remained
clickable. Changing the profile affects future messages, not the
in-flight response, so there is no reason to block it.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #56704

Release Notes:

- Fixed the `agent: toggle profile selector` keybinding being ignored
while the agent was generating a response.

---------

Co-authored-by: Danilo Leal <67129314+danilo-leal@users.noreply.github.com>