Harden backup creation and split maintenance jobs

[jsugg]

Summary

• move recovery backups to the StrongClaw state-backed backup root instead of ~/.openclaw/backups
• harden fallback archive creation with explicit backup-root exclusions and atomic temp-file promotion
• remove partial archive artifacts on create failure and keep restore safety checks intact
• split maintenance scheduling into independent create, verify, and prune jobs for both systemd and launchd
• align backup/recovery docs and repository contracts with the updated runtime behavior