feat(nixpacks): add Node.js 18 and pnpm to nixPkgs list

Enhanced the nixpacks configuration by including Node.js 18 and pnpm in the nixPkgs array, expanding the development environment capabilities.

nixpacks.toml

@@ -3,7 +3,9 @@ nixPkgs = [
   "python3",
   "pkg-config",
   "gnumake",
-  "gcc"
+  "gcc",
+  "nodejs_18",
+  "pnpm"
 ]