Model selector disappears when tab is moved to another panel

[apcamargo]

Check for existing issues

• Completed

Describe the bug / provide steps to reproduce it

• Open up the assistant panel.
• Move the assistant tab to a different panel. The model selector will be gone.

Zed Version and System Specs

Zed: v0.167.1 (Zed)
OS: macOS 15.2.0
Memory: 16 GiB
Architecture: x86_64

If applicable, add screenshots or screencasts of the incorrect state / behavior

After moving the tab to a different panel:

If applicable, attach your Zed.log file to this issue.

No response

[JosephTLyons]

I went ahead and triaged this issue, but it is likely that once our assistant rewrite is finished, this sort of thing will no longer be possible.