0bd3b52fb5
Implements the repo-side artifacts of Phase B5 (plans/implementation-plan-A-B.md). Creates 5 .service + .timer pairs under deploy/systemd/ that replicate the periodic tasks registered on Windows by scripts/Register-CIScheduledTasks.ps1: - ci-cleanup-orphans -> python -m ci_orchestrator vm cleanup --max-age-hours 6 (every 6h + boot) - ci-retention-policy -> pwsh Invoke-RetentionPolicy.ps1 (daily 03:00) - ci-watch-disk-space -> python -m ci_orchestrator monitor disk (every 15min) - ci-watch-runner-health -> python -m ci_orchestrator monitor runner (every 15min) - ci-backup-template -> pwsh Backup-CITemplate.ps1 (weekly Sun 02:00, NEW) Includes deploy/systemd/README.md with mapping table, install/test/rollback instructions, and PowerShell Core install note for the two PS-only scripts. Plan checklist updated; B5-closeout.md added. Hardware install steps (systemctl enable + smoke) remain user responsibility on the Linux host.