Public health snapshot. Returns each available Corent tier and whether it is operational, degraded, or down. Tier-level only.

Health is judged on RECENT real outcomes (provider_reliability, a 24-hour window), never on a stale lifetime failure counter. A tier is "down" only when every supplier behind it is actively failing recent customer jobs, or its supplier accounts are out of money; a resolved blip or a quiet day reads as operational, not a false alarm.