Guest Page with Program Return
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Upload/replace:

guest.php
assets/guest.css
assets/guest.js

This replaces the raw/default guest page with a professional layout and adds Program Return.

The guest page now:
- starts local camera/mic preview
- joins LiveKit backstage as guest
- publishes guest camera/mic
- subscribes to Program Output tracks:
  itahuka-program-video
  itahuka-program-audio
- displays Program Return in the right panel

How to test:
1. Open studio.php and connect operator.
2. Open guest.php?room=itahuka-live from another tab/device.
3. Start preview.
4. Join backstage.
5. In studio, add guest to stream.
6. Start Program Output.
7. Publish Program to LiveKit.
8. Guest should see Program Return.
