[FEAT] Export all reports in Deep Research mode

[JaimeParker]

• 当前Deep Research对话中，如果存在多个research结果，导出时json/markdown都无法全部导出，大多数情况是只导出当前的research，用json时有时能多导出几个，但没法全部导出
• In the current Deep Research conversation, if there are multiple research results, neither JSON nor Markdown can export all of them. In most cases, only the current research result is exported. When using JSON, sometimes more results can be exported, but not all of them.

[Nagi-ovo]

Deep Research isn’t well supported yet. We’ll work on it in the future, but also welcome related PRs!