Covers the WP 6.7 doing_it_wrong notice fired when a theme/plugin
translates before init (e.g. nav-menu labels on after_setup_theme).
Documents source fix (defer to init) and the update-safe mu-plugin
suppression via doing_it_wrong_trigger_error, plus the renamed-theme
domain gotcha. Derived from the majorlinux.com kappa/marstheme triage.
