add systemPrompts support

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Please confirm before submission 在提交之前，请确认

• I have searched for existing issues search for existing issues, including closed ones.
  我已经搜索了现有问题搜索现有问题，包括已关闭的问题。"

Is this request related to a challenge you're experiencing? Tell me about your story. 这个请求与你正在经历的挑战有关吗？给我讲讲你的故事。

Hi, Do you have any plan to add system prompts support?

大佬，有没有添加系统prompt的计划，类似Claude、Cursor一样，在配置里面添加 "systemPrompts" 字段来支持。

Can you help us with this feature? 你能帮我们实现这个功能吗？

• I am interested in contributing to this feature. 我有兴趣为这个特性做贡献。