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:

- Added "New Center Terminal" button to window context menu

"New Terminal" only opens a new terminal window in the dedicated
terminal view, while "New Center Terminal" opens a new terminal in the
currently active view.

"+"/"New..." context menu
<img width="487" height="318" alt="Screenshot_20260411_184840"
src="https://github.com/user-attachments/assets/7c1597cf-5638-4d76-a486-537033cb8da5"
/>

Right click context menu
<img width="422" height="386" alt="Screenshot_20260411_184904"
src="https://github.com/user-attachments/assets/4e557e21-8839-4226-b704-87e37fbd8f46"
/>