docs(readme): make English the default README

README.md carried the Chinese version while README.en.md held the English one,
so the GitHub landing page opened in Chinese. Swap them: README.md is now
English and the Chinese version lives in README.zh-CN.md, with both language
switchers pointing at the new paths.

scripts/pr/change-policy.test.ts

@@ -35,7 +35,7 @@ describe('evaluateChangePolicy', () => {
       'docs/index.md',
       'site/src/App.tsx',
       'README.md',
-      'README.en.md',
+      'README.zh-CN.md',
     ])
 
     expect(result.blocked).toBe(false)

scripts/pr/change-policy.ts

@@ -177,7 +177,7 @@ const policyExactPaths = new Set([
 
 const docsExactPaths = new Set([
   'README.md',
-  'README.en.md',
+  'README.zh-CN.md',
   'package.json',
   'package-lock.json',
   '.github/workflows/deploy-docs.yml',