Contacts can be marked private at submit time (single form, CSV
import, ADIF import) and edit time. Private contacts are hidden
from the public map, the public /u/callsign profile, and the
browse table for anonymous and non-owning viewers. The original
submitter and admins see them inline on the browse table with a
"Yes" badge, and the detail page shows a lock icon. Non-authorized
viewers get a 404 on the detail page.
