feat(i18n): add internationalization support

This commit introduces internationalization (i18n) support by integrating the `@nuxtjs/i18n` module. It configures English (en) and
Simplified Chinese (zh-CN) locales, adds a language selector to the header, and internationalizes the index page content using
translation files.

i18n/locales/en-US/index.json

@@ -0,0 +1,5 @@
+{
+  "index": {
+    "trustedBy": "Trusted by over {count} users worldwide"
+  }
+}