v1.35

v1.35: one way to install the desktop, and its menu shows up when it is there

The graphical session is installed with devbox dev-env desktop, like every environment. devbox desktop then joins the menu of devbox, with its own menu: the apps (VS Code, Chromium), start, stop.
Before that, and after a removal, devbox desktop stays out of the menu and the list.
devbox desktop enable and devbox desktop disable, added in v1.34, are gone: devbox dev-env desktop and devbox dev-env --remove desktop do it.