Get Pipeline Health

One glanceable read -- see app.modules.audit.health_surface's own module docstring for why this is DEMOTED: read-only, nothing here ever fixes anything, and it exists for Frederick to glance at when curious, never as the mechanism that notices or repairs a stalled pipeline (that is issues_service.release_stalled_builds, run independently on both the drain loop's own schedule and the audit cron's, plus the synthetic canary -- see tools/audit/run_once.py).