fix: add timeout to HTTP client in StarRocks stream load

The http.Client used for StarRocks stream load had no timeout configured,
which could cause requests to hang indefinitely. Add a 60-second timeout.

backend/plugins/starrocks/tasks/tasks.go

diff --git a/backend/plugins/starrocks/tasks/tasks.go b/backend/plugins/starrocks/tasks/tasks.go
index 79fbe5d..fab7517 100644
--- a/backend/plugins/starrocks/tasks/tasks.go
+++ b/backend/plugins/starrocks/tasks/tasks.go
@@ -394,6 +394,7 @@
 		return err
 	}
 	client := http.Client{
+		Timeout: 60 * time.Second,
 		CheckRedirect: func(req *http.Request, via []*http.Request) error {
 			return http.ErrUseLastResponse
 		},