A second launch handed its files to the running app, which could not raise its
window under GNOME's focus-stealing prevention. The launcher's activation token
(XDG_ACTIVATION_TOKEN, or DESKTOP_STARTUP_ID) now travels with the files, and the
running app activates its surface with xdg_activation_v1, or on X11 sends
_NET_ACTIVE_WINDOW at the launch's time and ends the startup notification. A
cold launch opens with the token too, and the desktop entry asks for startup
notification, without which GLib launchers pass no token.

Verified on Fedora Silverblue 44 (GNOME 50) by opening a second section from
Files over the running window, on Wayland and on Xwayland.

Fixes #58.

Assisted-by: claude-opus-5.5