Similar to the mode selector in external agents, it will now be possible
to use `shift-tab` to cycle through profiles.

<img width="500" height="384" alt="Screenshot 2025-12-16 at 9  04@2x"
src="https://github.com/user-attachments/assets/11e8824e-9fad-4aab-9e19-53878096db52"
/>

Release Notes:

- Added the ability to use `shift-tab` to cycle through profiles for the
built-in Zed agent.