Add a windows11 target that downloads the Windows 11 ISO with headless Chromium

Move the Node.js script and its dependencies into nodejs/ and let
download-images.sh call it for the image architecture.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitignore

@@ -13,3 +13,6 @@
 !base-qcow2/.gitkeep
 !install-iso/.gitkeep
 !tools-iso/.gitkeep
+
+# Node dependencies of nodejs/get-windows-iso-url.js.
+node_modules/