Add ClipCase handoff demo content

[rogerchappel]

Summary

• add a runnable ClipCase agent handoff demo using temporary storage
• document the casefile workflow with tutorial, video brief, and social hooks

Verification

• npm install
• npm run build
• bash examples/run-agent-handoff-demo.sh
• npm run check

Notes

• Initial build in the isolated worktree failed until dependencies were installed; package files were unchanged after npm install.