Closes AI-354

The "Panel Layout" submenu available in the user menu exposed two quick
menu items to switch between the classic and agentic workspace layout.
These will now also be available as actions, reachable through the
command palette.

<img width="600" alt="Screenshot 2026-06-01 at 8  28@2x"
src="https://github.com/user-attachments/assets/c468b958-9588-4646-a689-6e661a8f6e5a"
/>

Release Notes:

- Exposed actions to switch between the classic and agentic workspace
layout in the command palette.