fix(release): require complete release notes

[DarinRowe]

Summary

• restore the missing Cursor entry and privacy boundary in the v0.1.8 changelog
• require every PR to update [Unreleased] or explicitly declare Release-Note: none - <reason>
• add one deterministic release preparation command that promotes the full Unreleased section and synchronizes version metadata
• keep existing GitHub Release bodies synchronized when release assets are regenerated

Validation

• bun test (197 passed)
• bun run typecheck
• bun run package:agent-skill:check
• actionlint .github/workflows/*.yml
• bun run scripts/package-release.ts --version=v0.1.8 --cli-targets=host
• bun run package:release:test
• generated v0.1.8 release notes contain Cursor functionality and privacy exclusions