fix build bug

app/utils/stream.ts

@@ -69,7 +69,8 @@ export function fetch(url: string, options?: RequestInit): Promise<Response> {
     const headers: Record<string, string> = {
       Accept: "application/json, text/plain, */*",
       "Accept-Language": "en-US,en;q=0.9,zh-CN;q=0.8,zh;q=0.7",
-      "User-Agent": navigator.userAgent,
+      "User-Agent":
+        typeof navigator !== "undefined" ? navigator.userAgent : "NextChat",
     };
     for (const item of new Headers(_headers || {})) {
       headers[item[0]] = item[1];