Fix and improve automatic i3 layout

hosts/desktop/i3/default.nix

@@ -1,10 +1,14 @@
-{ ... }:
+{ pkgs, ... }:
 
 {
   xsession.windowManager.i3.config = {
     startup = [
       {
-        command = ''i3-msg workspace 1 && (firefox &) && i3-msg "workspace 2; append_layout ${./tree.json}; open" && (for i in {1..4}; do i3-msg move left; done) && (discord &) && firefox --new-window https://youtube.com && i3-msg workspace 1'';
+        command = let layout = pkgs.substituteAll {
+          src = ./layout.sh;
+          tree = ./tree.json;
+          isExecutable = true;
+        }; in "${layout}";
         always = true;
         notification = false;
       }

hosts/desktop/i3/layout.sh

@@ -0,0 +1,10 @@
+i3-msg workspace 1
+firefox &
+
+i3-msg "workspace 2; append_layout @tree@; open"
+for i in {1..4}; do
+    i3-msg move left
+done
+discord
+firefox --new-window https://youtube.com
+i3-msg workspace 1