feat: add fal H3 Max free video handoff

[atomantic]

Summary

• Add a browser-only MiniMax H3 Max handoff to Video Gen and each FableLoom scene using PortOS composed prompts.
• Import downloaded MP4 renders into shared Media History and attach them to FableLoom scenes.
• Keep fal API billing out of the free flow and provide a manual prompt fallback when clipboard access is unavailable.

Test plan

• cd client && npm test
• cd client && npm run build