Clarify maintainer positioning and quick demo

[TheRobertRay]

Summary

• Add README badges, sharper maintainer use cases, and a practical "What You Can Use Today" table.
• Add docs/quick-demo.md so reviewers and maintainers can validate the kit, temp-install one skill, and try a no-write receipt prompt.
• Wire the quick demo into repository validation and the changelog.

Validation

• bash scripts/validate.sh
• bash scripts/check-publication-risk.sh
• FORBIDDEN_TERMS='Hermes,Josh,Telegram,Robert OS,/Users/robertray' bash scripts/check-publication-risk.sh
• temp-target install of conversation-capture-receipts
• git diff --check
• reviewer pass with no blockers

Closes #8