valw: overview backdrop and window picker

modules/home/niri/desktop-niri-execs.ulu.nix

@@ -7,6 +7,8 @@
         "prefer-no-csd" = true;
         spawn-at-startup = [
           { command = [ "noctalia" ]; }
+          # valw's paint shader behind the overview (see the layer rule).
+          { command = [ "valw" "backdrop" ]; }
         ];
       };
     };