feat(window): close other / left / right project tabs from the window-group tab menu (#965)

Right-clicking a project tab in a merged window group offers Close Other Tabs, Close Tabs to the Left and Close Tabs to the Right (left/right disabled at the ends); the same commands are in the Command Palette and can take shortcuts.

The backend closes the projects one at a time, focusing each so its own unsaved-changes prompt is visible, as Quit does. Cancelling a prompt stops the batch and leaves that project and the rest open; the clicked tab stays and is selected when the batch finishes. Starting Quit clears a pending batch.

Closes #942.

Co-authored-by: jaw52 <[email protected]>

docs/workspaces-and-window-groups.md

@@ -28,7 +28,7 @@ The specialized Maven/Gradle tool-window model still describes the workspace dir
 
 Open two project windows, then use **Window → Merge All Project Windows**. The project tabs occupy their own row below the main toolbar. Click a tab or use **Next/Previous Project Tab** to switch; drag tabs to reorder them. The default shortcuts are ⌥⌘PageDown/PageUp on macOS and Ctrl+Alt+PageDown/PageUp on Windows/Linux.
 
-Use the tab's close button to close that project, or **Move Tab to New Window** to detach the current tab. Closing uses the existing unsaved-changes guard. Quit visits project windows in sequence so a hidden project's prompt is visible. Groups restore when **Reopen last project** is enabled.
+Use the tab's close button to close that project, or **Move Tab to New Window** to detach the current tab. Right-click a tab for **Close Other Tabs**, **Close Tabs to the Left** and **Close Tabs to the Right**, which close the projects one at a time and keep the clicked tab; cancelling one project's unsaved-changes prompt leaves it and the rest open. The same commands are in the Command Palette and can be assigned shortcuts. Closing uses the existing unsaved-changes guard. Quit visits project windows in sequence so a hidden project's prompt is visible. Groups restore when **Reopen last project** is enabled.
 
 The grouping model lives in `ide-workspace`, independently of project ownership. The desktop adapter keeps each member's WebView and backend services alive, presents the selected window at the group's position/size, and hides its peers. This is an application-drawn tab strip, not the macOS native tab strip. Its persistence is application-local in `window-groups.json`. Language servers, terminals, editor buffers and settings remain independent between group members.