Addresses PR review: on a native Linux/SSH session with neither DISPLAY
nor WAYLAND_DISPLAY (and not Docker/WSL), _open_path unconditionally
launched xdg-open and reported success even though no file manager can
open. Mirror open_settings_location: hand the path to the browser for
copying instead. Fixes open_backup_location, open_wildcards_location
and open_sidecar_location together.