docs: add support handoff demo pack

[rogerchappel]

Summary

• add a temporary-storage support handoff demo recipe
• add social hooks and demo beats grounded in the README command set
• link the demo and promo pack from the README

Verification

• npm install
• npm run build
• CLIPCASE_HOME=/tmp/clipcase-demo node dist/src/cli.js init --storage /tmp/clipcase-demo/cases
• CLIPCASE_HOME=/tmp/clipcase-demo node dist/src/cli.js new login-redirect --title "Login redirect repro"
• piped repro and terminal text into clipcase add with source and tag labels
• CLIPCASE_HOME=/tmp/clipcase-demo node dist/src/cli.js search redirect
• CLIPCASE_HOME=/tmp/clipcase-demo node dist/src/cli.js export login-redirect --out /tmp/clipcase-demo/handoff.md

Known validation blocker

• bash scripts/validate.sh currently fails in the existing test suite because dist/test/cli.test.js expects unsupported legacy commands: list formats, convert, and detect. The new demo command path above passed before that existing validation failure.