URL Health Check - Batch (up to 10 URLs)

Same verdicts as our single-URL check (LIVE, PAUSED, DEGRADED, GATED, DOWN, DEAD, UNKNOWN), for up to 10 URLs in one call. Send {"urls": ["https://...", ...]} (max 10). Each result carries its own verdict, reason and source - a front door answering 200 over a stalled backend is still flagged, per-URL, via the origins own health/heartbeat surface when it publishes one. Useful for a preflight sweep of several dependencies at once instead of one call per URL.