docs: update Discord invite link across all README files

- Update Discord invite from discord.gg/aSfGzWtYxM to discord.gg/PUwSMR9XNk
- Synchronized across all language variants:
  - README.md (English)
  - README.ko.md (Korean)
  - README.ja.md (Japanese)
  - README.zh-cn.md (Simplified Chinese)

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

README.zh-cn.md

@@ -7,7 +7,7 @@
 >
 > 与我们同行！
 >
-> | [<img alt="Discord link" src="https://img.shields.io/discord/1452487457085063218?color=5865F2&label=discord&labelColor=black&logo=discord&logoColor=white&style=flat-square" width="156px" />](https://discord.gg/aSfGzWtYxM) | 加入我们的 [Discord 社区](https://discord.gg/aSfGzWtYxM)，和贡献者们、`oh-my-opencode` 用户们一起交流。 |
+> | [<img alt="Discord link" src="https://img.shields.io/discord/1452487457085063218?color=5865F2&label=discord&labelColor=black&logo=discord&logoColor=white&style=flat-square" width="156px" />](https://discord.gg/PUwSMR9XNk) | 加入我们的 [Discord 社区](https://discord.gg/PUwSMR9XNk)，和贡献者们、`oh-my-opencode` 用户们一起交流。 |
 > | :-----| :----- |
 > | [<img alt="X link" src="https://img.shields.io/badge/Follow-%40justsisyphus-00CED1?style=flat-square&logo=x&labelColor=black" width="156px" />](https://x.com/justsisyphus) | `oh-my-opencode` 的消息之前在我的 X 账号发，但账号被无辜封了，<br />现在 [@justsisyphus](https://x.com/justsisyphus) 替我发更新。 |
 > | [<img alt="Sponsor" src="https://img.shields.io/badge/Sponsor-❤-ff69b4?style=flat-square&logo=github-sponsors&labelColor=black" width="156px" />](https://github.com/sponsors/code-yeongyu) | [成为赞助者](https://github.com/sponsors/code-yeongyu)，支持 `oh-my-opencode` 的开发。您的支持让这个项目持续成长。 |