v1.2.1

Name the desktop entry after the GTK application id

GNOME Shell matches a running Wayland window to its launcher by
looking up <app-id>.desktop; the entry was installed as
secureshellgo.desktop while the runner identifies as
com.dhivalabs.secure_shell_go, so the running app fell back to the
generic gear icon in the dock. Rename the installed entry to match
and fix StartupWMClass to the real WM_CLASS (prgname is set to the
application id — verified with xprop under XWayland: instance
com.dhivalabs.secure_shell_go), covering X11 sessions too.

Bump to 1.2.1.