feat(desktop): add the rofi launcher (task 0024)

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 fade-in (layersIn and fadeLayersIn)
at the window animation speed, so the launcher fades in quickly rather
than snapping into place.

modules/desktop/hyprland/hyprland.nix

@@ -98,6 +98,9 @@ in
           animation = [
             "windows, 1, 3, ease"
             "fade, 1, 3, ease"
+            # Layer surfaces like the launcher fade in a touch quicker than windows.
+            "layersIn, 1, 2, ease"
+            "fadeLayersIn, 1, 2, ease"
             "workspaces, 1, 3, ease"
             "border, 1, 3, ease"
           ];