Add syairag/siyuan-ai-assistant

[syairag]

If you are submitting a new bazaar package for the first time, please confirm the following information.

• The repository is public
• Include the appropriate open source license file LICENSE
• Does not involve infringing content, such as non-commercial font files

If your marketplace package is closed-source, please grant @TCOTC, @88250, and @Vanessa219 access to the source code so that we can complete the review.

[TCOTC]

• 按照说明修正 plugin.json 文件：https://github.com/siyuan-note/plugin-sample/blob/main/README_zh_CN.md#pluginjson
• 仓库中没有看到原始代码，请向我提供源码