surveyadmin create admin without a startup script

We should just look for the presence of an admin user when we check authentication, and indicate what variables must be set up in this case
Tying auth check and admin creation would prevent any risk of running the app without an admin forgetting to set it up etc.

Locate the surveyadmin authentication check and the admin-creation flow, then inspect how startup variables are currently read. The work is done when authentication detects whether an admin exists, clearly indicates the variables that must be set, and prevents the app from running without an admin.

Written by the indexing model from the issue text.