docs(readme): make Chinese the default README and keep only the film (#1436)

- README.md is now Chinese; the English README moves to README.en.md.
- Drop the eight-screenshot grid and the Agent Teams loop; the film cover
  remains the single visual. Remove the now-unused thumbnails.
- Point PR triage, change policy, and the docs check at the new file names.

site/scripts/check-docs.mjs

@@ -272,8 +272,8 @@ async function checkLocaleRedirect() {
 async function main() {
   const { records } = await generateDocsManifest()
   const readmes = await Promise.all([
-    { locale: 'en', sourcePath: 'README.md' },
-    { locale: 'zh', sourcePath: 'README.zh-CN.md' }
+    { locale: 'en', sourcePath: 'README.en.md' },
+    { locale: 'zh', sourcePath: 'README.md' }
   ].map(async (readme) => {
     const absolutePath = path.join(paths.repoDir, readme.sourcePath)
     return {