Rename zh-CN to cn for Chinese docs and i18n

Migrates all Chinese documentation files and related configuration from 'zh-CN' to 'cn' for consistency. Updates i18n config, CLI, workflows, and site logic to use the new 'cn' code. Removes unused site root layout and redirect components, and adds i18n middleware proxy for language routing.

Author: hotlong

.github/labeler.yml

@@ -7,7 +7,7 @@ documentation:
 i18n:
   - changed-files:
     - any-glob-to-any-file:
-      - 'content/**/*.zh-CN.mdx'
+      - 'content/**/*.cn.mdx'
       - 'content/**/*.en.mdx'
       - 'lib/i18n.ts'
 

.github/workflows/ai-translate.yml

@@ -57,8 +57,8 @@ jobs:
         uses: peter-evans/create-pull-request@v6
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          commit-message: "docs: auto-translate updates to zh-CN"
-          title: "🤖 Auto Translate: Sync zh-CN docs"
+          commit-message: "docs: auto-translate updates to cn"
+          title: "🤖 Auto Translate: Sync cn docs"
           body: |
             This PR automatically syncs the Chinese documentation with the latest English changes.
             

.github/workflows/preview.yml

@@ -28,7 +28,7 @@ jobs:
             
             ### Preview Links
             - 📝 **Documentation**: Will be available once Vercel deployment completes
-            - 🌍 **Languages**: English (\`/en/docs\`) and Chinese (\`/zh-CN/docs\`)
+            - 🌍 **Languages**: English (\`/en/docs\`) and Chinese (\`/cn/docs\`)
             
             ### Build Status
             Check the CI workflow for build status and any errors.