fix(service): convert web readable stream to node stream in text2Speech (#6985)

packages/service/core/ai/audio/speech.ts

 import type { NextApiResponse } from 'next';
 import { getAIApi } from '../config';
 import { getTTSModel } from '../model';
+import { Readable } from 'stream';
 
 export async function text2Speech({
   res,
@@ -40,7 +41,11 @@ export async function text2Speech({
       : {}
   );
 
-  const readableStream = response.body as unknown as NodeJS.ReadableStream;
+  if (!response.body) {
+    throw new Error('Response body is empty');
+  }
+
+  const readableStream = Readable.fromWeb(response.body as Parameters<typeof Readable.fromWeb>[0]);
   readableStream.pipe(res);
 
   const chunks: Uint8Array[] = [];