F24-1: resolve refs/remotes/origin/main^{commit} instead of the ambiguous
origin/main, which a tag or local branch of that name would shadow.
F24-2: the timer fires on OnCalendar=*-*-* *:0/15:00 so Persistent=true
catches up a check missed while the host was down; the runbook documents
the new schedule.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>