Closes#968 on stable. Backport of #974.
The roles-join fallback in adminAuth fabricated role_name='super_admin' on ANY database error, so a transient fault silently granted super_admin for its duration. Gate it on isMissingRolesSchema(), moved to utils/dbErrors.js and shared with apiTokenAuth, with the predicate tightened to trust SQLSTATE 42P01/42703 on Postgres and exact driver phrasing on SQLite.
Paul Nothaft