fix(tts): use temporary file for WAV encoding to avoid BytesIO limitation

fix(UniverPreview): update error messages and hints for document loading

backend/tts_asr.py

@@ -214,10 +214,17 @@ async def tts_endpoint(req: TTSRequest):
 
     # 编码 WAV 到内存
     try:
+        import tempfile
         import soundfile as sf
-        bio = BytesIO()
-        sf.write(bio, wav_data, sr, format="WAV")
-        audio_bytes = bio.getvalue()
+        # soundfile 不支持直接写入 BytesIO，需要用临时文件
+        with tempfile.NamedTemporaryFile(suffix=".wav", delete=False) as tmp:
+            tmp_path = tmp.name
+        sf.write(tmp_path, wav_data, sr, format="WAV")
+        with open(tmp_path, "rb") as f:
+            audio_bytes = f.read()
+        # 清理临时文件
+        import os as _os
+        _os.unlink(tmp_path)
     except Exception as e:
         logger.exception("音频编码失败")
         raise HTTPException(status_code=500, detail=f"音频编码失败: {e}")