希望能支持隐藏底部模型选择栏

[omega-leo]

在电脑和手机端这个模型选项占了和输入框一样的空间，但是除了新开对话其余时候都不太需要切换模型，这也导致大量纵向面积的浪费（尤其是手机端）！希望添加一个手动隐藏按钮或者自动隐藏的小三角悬浮标签。

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Title: Hope to support hidden bottom model selection bar

The model option on the computer and mobile terminals occupies the same space as the input box, but except for the newly opened dialogue, there is no need to switch the model, which also leads to a lot of waste of vertical area (especially on the mobile terminal)! Want to add a manual hidden button or a small triangle floating label that hides automatically.