修复图片微调报错

backend/app/engines/vision_engine.py

@@ -94,6 +94,8 @@ class VisionEngine(BaseEngine):
         # 写入输出（保留 image_path / label 等字段原样）
         output_p = Path(output_path)
         output_p.parent.mkdir(parents=True, exist_ok=True)
+        if output_p.exists():
+            output_p.unlink()
         with open(output_path, "w", encoding="utf-8") as f:
             for item in data:
                 f.write(json.dumps(item, ensure_ascii=False) + "\n")