On macOS, `hermes update` and `hermes desktop` reinstall any Hermes.app
listed in desktop-installed-apps.json that has gone missing, and the GUI
uninstall is what deletes that record. gui_is_installed() ignored the
record, so after the app was removed by hand `hermes uninstall --gui`
reported that no GUI was installed and returned without deleting it, and
the next update put the app back.
Count the install record in gui_is_installed() so the uninstall previews
and removes it. No new removal targets: uninstall_gui() already deletes
the record. The retention tests now also run with the record as the only
remaining GUI artifact.
Refs: #128974
Salvaged-from: #131147
80efaa56ee