Wagtail's initial migration creates a localhost:80 site. Wagtail matches
incoming requests by hostname before ever checking is_default_site, so
updating only the is_default_site record left localhost:80 still pointing
at the Welcome page. Fix by updating root_page on every site.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
