Add green_screen_processor (auto-detect + rembg fallback) and
green_screen_composite (4 layout presets with alpha compositing) tools
to automate the full keying-to-composite pipeline.
Remotion: add AnimatedBackground with gradient mesh and floating orbs
to Explainer, fix caption burn tool (remove entry point arg, auto-detect
dimensions, extend TalkingHead duration to 300s).
Update scene-director, compose-director, and asset-director skill docs
with green screen workflow steps and component constraints.