feat: add tags to articles, full i18n coverage, and Tailwind CSS setup

- Add tag frontmatter to all 6 blog articles (3 articles × 2 locales)
- Complete i18n.json with all 26 text keys for en-gb and zh-hans
- Install and configure Tailwind CSS v4 with PostCSS
- Create Tags component using Tailwind utility classes
- Inject Tags into DocLayout via theme override
- Fix zh-hans homepage icon extension

theme/index.tsx

@@ -1,3 +1,20 @@
 import './index.css';
+import { DocLayout as OriginalDocLayout } from '@rspress/core/theme-original';
+import { Tags } from './components/Tags';
+
+function DocLayout(props) {
+  return (
+    <OriginalDocLayout
+      {...props}
+      beforeDocContent={
+        <>
+          <Tags />
+          {props.beforeDocContent}
+        </>
+      }
+    />
+  );
+}
 
 export * from '@rspress/core/theme-original';
+export { DocLayout };