fix: update plugin marketplace URL in documentation

[stevessr]

看起来旧的地址已经无法访问……

Sourcery 摘要

更新文档，将主站和插件市场的过时 .top 域名 URL 替换为新的 .app 域名。

文档：

• 将 README 中的主文档链接从 https://astrbot.soulter.top 更改为 https://docs.astrbot.app
• 在英文和中文插件发布指南中，将 AstrBot 插件市场 URL 从 https://plugins.astrbot.top 更新为 https://plugins.astrbot.app

Original summary in English

Summary by Sourcery

Update documentation to replace outdated .top domain URLs with the new .app domain for the main site and plugin marketplace.

Documentation:

• Change the main documentation link in README from https://astrbot.soulter.top to https://docs.astrbot.app
• Update the AstrBot Plugin Marketplace URL in both English and Chinese plugin-publish guides from https://plugins.astrbot.top to https://plugins.astrbot.app

[sourcery-ai]

你好 - 我已审阅了你的更改，它们看起来很棒！

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Original comment in English

Hey there - I've reviewed your changes and they look great!

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[Soulter]

感谢修正！