Add top-level `vmgui` to open the VMware Workstation GUI (renamed from the
earlier `vm open`). --vmx is optional: with it the GUI opens that VM, without
it the GUI starts bare. Power-on/fullscreen flags ignored (with a notice) when
no VMX is given. Needs an X display — sudo -u ci-runner strips $DISPLAY, so
--display / xhost; see runbook §4.7. 9 tests; suite green ≥90%.