fix: unify chinese language code as zh-CN

src/components/messageStream/MessageStream.tsx

@@ -26,7 +26,7 @@ export function MessageStream({ scope }: MessageStreamProps) {
   const { items, isLoading, error, hasMore, loadMore, reset } =
     usePostStream(params);
   const groups = useGroupedByDay(items, lang);
-  const retryLabel = lang === "zh" ? "重试" : "Retry";
+  const retryLabel = lang === "zh-CN" ? "重试" : "Retry";
 
   const sentinelRef = useRef<HTMLDivElement>(null);
   const hasMoreRef = useRef(hasMore);