Consider keeping sidebar state when opening modals via native dialog.

[acelaya]

For historical reasons, we have been hiding the sidebar when modals like the notebook were opened. However, we have recently refactored it to use a native dialog element, opened via dialog.showModal().

This provides proper focus trapping on the dialog itself, natively handled by the browser, which means we could keep the sidebar as is, reducing the complexity and cross-frame communication logic involved in opening/closing the notebook.

However, it would be good to check if there were some reason for this to be implemented using this approach, other than the lack of focus trapping.