The standalone empty state showed the folder_paths keys but not where to
put them, and its Open Settings button led to a modal that cannot edit
primary folder paths. Now the page shows the real settings.json path and
an Open Settings Folder button backed by the existing open-location API.
Also stop open_settings_location from claiming success on headless Linux
sessions: with no DISPLAY/WAYLAND_DISPLAY, xdg-open cannot work, so the
handler now returns clipboard mode and the browser copies/shows the path
instead.