Program Smoothness Fix

Replace:
assets/studio.js

Changes:
- Program Output no longer draws from visible Program preview videos.
- It uses dedicated hidden mixer video elements for each staged guest.
- Output render loop uses requestAnimationFrame with fixed 30fps pacing.
- Canvas context uses desynchronized rendering where browser supports it.
- captureStream frame request is called after each rendered frame.
- Mixer videos are recovered after focus/visibility changes.

This should make Program Output smoother and closer to the preview.
