Reapply 2026 SCC showcase wall with SSG fix

[zongen01]

这次是在已经回滚后的 main 基础上，重新提交 2026 SCC 展示墙，并修复正式部署时的静态构建错误。

主要内容：

• 恢复 2026 SCC Rabbita 展示墙页面与赛事页入口
• 保留之前为 showcase 增加的构建接线（build / dev / build script / asset ignore）
• 保留 moon.pkg / moon.pkg.json 的监听修复
• 修复 Docusaurus SSG 失败问题：将 RabbitaShowcaseMount 从 src/pages 路由目录移到 src/components，避免它被当成独立页面渲染，从而触发 useColorMode provider 错误

背景：

• 上一版展示墙 PR 合并后，Release 工作流在构建 /2026-scc/showcase/RabbitaShowcaseMount 时失败
• 这次 PR 专门解决该问题，并保留展示墙原始实现

说明：

• 我这边当前环境仍然没有 node / pnpm 可执行命令，因此无法本地直接跑完整 Docusaurus build
• 这次修复主要依据线上 Release 日志定位并收敛到最小改动

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6564691a04

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Route official-site CTA to locale-matching domain

link_official_site() always returns https://www.moonbitlang.com/2026-scc, so on Chinese pages (document.documentElement.lang starts with zh) the localized “查看赛事官网” button still sends users to the English domain. This is a user-facing localization regression introduced with the new showcase app, and the URL should be selected via lang(...) (or equivalent locale-aware routing) so zh users stay on the zh site.

Useful? React with 👍 / 👎.