[Other] Allow exporting reasoning content。增加导出思考部分内容

[LawrentChen]

Currently, the chat history export only includes system, user, and assistant messages. It would be beneficial to incorporate the thought process content as well. I'm using the deepseek-r1 api from aliyun, and while the chatbox interface correctly displays the reasoning content, it is absent in the exported data.

导出聊天记录目前只会导出 system, user, assistant。希望可以增加导出思考内容 我使用的是阿里云的 deepseek-r1 api，chatbox图形界面上可以正确显示思考内容，但导出记录里没有

[pisceswb]

+1 思考内容中也有想要保存的，我的诉求是至少能选中复制，不像现在，点击一下就折叠。

[hiking93]

+1 如果 tool call 也能 export 就太棒了 我的對話裡時常只有 tool call 跟 thinking，export 以後基本上空白一片