Fixes #42668

When clicking 'Configure' to enter a settings subpage, focus was being
lost because push_sub_page only called cx.notify() without managing
focus. Similarly, pop_sub_page had the same issue when navigating back.

This fix:
- Adds window parameter to push_sub_page and pop_sub_page
- Focuses the content area when entering/leaving subpages
- Resets scroll position when entering a subpage

Release Notes:

- Fixed a bug that prevented keyboard navigation in the settings window.