Too easy to create sites which do not syndicate

Currently, to create a new RSS pull site, you must assign it to a site group for anything to work. This is not obvious to the user; we do not show an error, nor do we assign default site groups.

Suggestion: We should create a default site group, then we should assign all auto-draft sites to that default site group.

Start by tracing how new RSS pull sites and auto-draft sites are created, then follow where site groups are assigned. Verify the default site-group behavior and identify the existing checks or tests around syndication setup. Done means newly created auto-draft sites are assigned to a default group and syndicate without manual setup.

Written by the indexing model from the issue text.