Brings stable logout and additional directories support as well as
removing dep on rmcp + tokio

This also removed the unstable model selector (replaced awhile ago by
session config options) so it removes all of that code.

Native agent still uses it because we have a special model selector that
would need more work to rip out

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

Release Notes:

- N/A