WIP: Spike adding Scratch project type

[floehopper]

There's a corresponding branch in editor-standalone that adds a /scratch-project path that can be used to view the Scratch UI. This works because the Cloudflare Pages configuration for the editor-standalone branch is pointing at the deployment of this editor-ui branch in Cloudflare R2.

Note that we set cross-origin-embedder-policy to cross-origin in the dev server config so that we can render the scratch-editor.pages.dev page in our iframe in the web-component.html test page.

Things to do before we can merge

• Work out how to view Scratch projects vs Python and HTML projects
• Decide who should be able to see the Scratch editor
• Configure cross-origin headers to securely allow scratch-editor.pages.dev to be embedded in the iframe
• Add tests