Mirrors the deploy-log pattern: deployer writes 15-staging-log.md on the
feature branch, then merges the artifact into origin/main so the
check_staging_status quality gate can read it via _staging_log_from_main()
(see src/qg/checks.py:489).
Verdict from the staging run on http://localhost:8501 (mode=stub):
staging_status: SUCCESS (10/10 checks PASS)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
