Add release boundary demo content

[rogerchappel]

Summary

• add a runnable release-note write boundary demo script
• add JSONL write candidates and tutorial documentation
• add a grounded launch-note draft for promotion

Verification

• bash demo/release-note-boundary.sh

Notes

• The batch command is expected to return non-zero because the fixture includes denied paths; the demo verifies expected allow, deny, and outside-root reason codes.