fix: inline Three.js + characters.js into srcdoc iframe

fix: add allowed_paths=[sandbox_cache] to demo.launch()

fix: use file-served iframe src instead of srcdoc

fix: render studio in iframe srcdoc to isolate styles, pre-render on load

fix: disable SSR mode — breaks JS-heavy components (Three.js, bridge)

feat: Immersive Vibe Development Studio — initial release