fix: initialize circuit breaker gauge to CLOSED on startup

cmd/ingestd/main.go

@@ -80,6 +80,8 @@ func main() {
 	cb.Measure = func(state int, err error) {
 		m.CBState.WithLabelValues("nats").Set(float64(state))
 	}
+	// Initialize gauge to CLOSED (0) so Prometheus sees the metric before first transition.
+	m.CBState.WithLabelValues("nats").Set(0)
 	logger.Info("circuit breaker configured",
 		"failure_threshold", cfg.CircuitFailureThreshold,
 		"failure_window_sec", cfg.CircuitFailureWindowSecs,