Add 3D printing home role with orca-slicer and openscad

Create a new home-manager role for 3D printing applications including
orca-slicer for slicing and openscad-unstable for 3D modeling. Enable
the role in the desktop configuration for full-featured experience.

home/roles/3d-printing/default.nix

@@ -0,0 +1,22 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.home.roles."3d-printing";
+in
+{
+  options.home.roles."3d-printing" = {
+    enable = mkEnableOption "Enable 3D printing applications and tools";
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = with pkgs; [
+      # 3D Slicing Software
+      orca-slicer  # G-code generator for 3D printers (Bambu, Prusa, Voron, etc.)
+
+      # 3D Modeling Software
+      openscad-unstable  # 3D parametric model compiler (nightly build)
+    ];
+  };
+}