Add a "page" for the login screen
There should be some information on the login screen. This could just be a "page". It needs to be marked somehow so that it can not be deleted, and it will not show up among the regular pages.
To open for more pages in the same vein, just add a field called system with a string value determining what its use is. Any page with the system field set will be undeleteable and will not show up among the user pages. They could also be presented separately in the admin interface.
Pleceholders for these pages should be generated on the first startup.