- create_runtime_backup() now auto-validates its output and includes
validated/validation_errors fields in returned metadata
- New cleanup_old_backups() with retention policy: 7 daily, 4 weekly
(Sundays), 6 monthly (1st of month), dry-run by default
- CLI `cleanup` subcommand added to backup module
- 9 new tests (2 validation + 7 retention), 259 total passing
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>