LAB: nightly workflows need timeout-minutes + end by 05:00Z; reaper must catch queued/scheduled runs #5847

Operator 11:04Z (relayed): Lab/nightly workflows get timeout-minutes and must end by 05:00Z. Reaper must catch queued + scheduled runs. This PR: scripts/check_lab_timeouts.sh (RED on 24 findings, GREEN after) + timeouts/cron shifts. Reaper change tracked separately (deployed script ~/.local/libexec/pr-run-reaper.sh, source repo not in aprender).