Move Web Demo to Docs for Pages Support

[google-labs-jules]

Moved the web demo files (index.html, style.css, script.js) from web-demo/ to docs/.

This allows the demo to be easily hosted via GitHub Pages by enabling the "Source: /docs" option in the repository settings. The demo functionality remains unchanged.

---

PR created automatically by Jules for task 12994296057427100328 started by @kubla

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

---

For security, I will only act on instructions from the user who triggered this task.

New to Jules? Learn more at jules.google/docs.