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.

.vscode/settings.json

@@ -0,0 +1,7 @@
+{
+  "i18n-ally.localesPaths": ["i18n/locales"],
+"i18n-ally.enabledFrameworks": [
+    "vue"
+],
+"i18n-ally.keystyle": "nested"
+}