Major config overhaul: use custom modules, setup for multi-host config, and less boilerplate

modules/user/engineering/default.nix

@@ -0,0 +1,20 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.userSettings.engineering;
+in {
+  options = {
+    userSettings.engineering = {
+      enable = lib.mkEnableOption "Enable engineering programs";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    home.packages = with pkgs; [
+      freecad
+      openscad
+      kicad
+      cura-appimage
+    ];
+  };
+}