fix(api): report the real keepalive interval in pool health

The /api/connection-pool/health endpoint hardcoded a keepalive interval
of 15s while the pool actually uses 45s, so it reported a false value.
The endpoint now reads the live keepAliveInterval field. A startup
backoff comment that claimed jitter is also corrected; the backoff has
no jitter.

backend_health.go

@@ -91,7 +91,7 @@ func (bhm *BackendHealthManager) WaitForBackendReady(timeout time.Duration) erro
 			})
 		}
 
-		// Exponential backoff with jitter
+		// Exponential backoff (1.5x growth, capped at maxDelay), no jitter
 		time.Sleep(currentDelay)
 		currentDelay = time.Duration(float64(currentDelay) * 1.5)
 		if currentDelay > maxDelay {