Fix sgl-router startup crash (#7619)

sgl-router/src/router.rs

@@ -180,7 +180,15 @@ impl Router {
             }
             _ => {
                 // Wait until all workers are healthy for regular modes
-                Self::wait_for_healthy_workers(&worker_urls, timeout_secs, interval_secs)?;
+                let worker_urls = worker_urls.clone();
+                std::thread::spawn(move || {
+                    Self::wait_for_healthy_workers(&worker_urls, timeout_secs, interval_secs)
+                })
+                .join()
+                .map_err(|e| {
+                    error!("Health-check thread panicked: {:?}", e);
+                    format!("Health-check thread panicked: {e:?}")
+                })??;
             }
         }