`hermes backup` recorded per-file failures, printed `Backup incomplete: <path>`
and still returned shell status 0, so a cron job or systemd timer would publish
"successful" archives missing state.db indefinitely.
`run_backup()` now returns whether the archive is complete and `cmd_backup()`
maps False to exit status 1. The zip is kept so the operator can still restore
the rest; hard failures keep their SystemExit(1)/(2). `--quick` is unchanged.
Slim redo of #101096 on current main (the branch predates the run_backup /
_run_backup_locked split and the backup lock); same policy, same exit codes.
Supersedes #68866 (@jbryce) which proposed the policy first.
ccb3d968ce