Add a rofi module to the desktop group, enabled by the aggregator.
It runs the drun application launcher, bound on Super+R. A session menu
built on the same themed rofi is bound on Super+Shift+X, and every
rofi -dmenu call inherits the Stylix theme, so later utility menus
reuse it for free.
Also give layer surfaces their own near-instant fade-in (layersIn and
fadeLayersIn), so the launcher appears quicker than the windows it
sits over.
