restoring a backup does not restore deleted scans from that backup

Steps to reproduce:

• take some scans
• export a backup zip file
• delete a scan
• restore the backup

Current behavior is that the deleted scan stays deleted.

Users might expect to be able to recover deleted pages this way.

There are a couple of options for handling this better. One is to prompt the user to ask if scans should be restored. This would trigger if there are scans marked as deleted in the app, that are not marked as deleted in the backup. The prompt asks the user if those scans should be restored, ideally with options for selectively restoring.

The other option is to offer an "undelete" feature. That could go along with a "move to trash" strategy instead of immediately deleting. Restoring the backup gives you another change to undelete in case the undeletion window in the app has expired. The advantage of this approach is that it doesn't require user action right at the restore point, which would work better with cloud sync which runs in the background.