Fix mobile back navigation for work item panels

What does this MR do and why?

Mobile users can close a child work item panel with the browser Back button. The shared panel now handles the history entry it creates instead of relying on each parent view to close it.

References

None.

Screenshots or screen recordings

Before

After

How to set up and validate locally

1. Open a work item with a child item at a mobile viewport size.
2. Open the child item in the panel.
3. Use the browser Back button.
4. Confirm the panel closes and the parent work item remains open.

MR acceptance checklist

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