Remove Chinese language support and documentation

Removed Chinese ('cn') from supported languages in i18n configuration and deleted extensive documentation files, including guides, FAQs, advanced topics, and field type references. This streamlines the documentation to English-only and removes related content and metadata for the Chinese locale.

Author: hotlong

apps/docs/lib/i18n.ts

@@ -9,7 +9,7 @@ import { defineI18n } from 'fumadocs-core/i18n';
  */
 export const i18n = defineI18n({
   defaultLanguage: 'en',
-  languages: ['en', 'cn'],
+  languages: ['en'],
   // Hide locale prefix for default language (e.g., /docs instead of /en/docs)
   hideLocale: 'default-locale',
 });