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/components/Tags.tsx

@@ -0,0 +1,20 @@
+import { useFrontmatter } from "@rspress/core/runtime"
+
+export function Tags() {
+  const { frontmatter } = useFrontmatter()
+  const tags: string[] | undefined = frontmatter?.tags as string[]
+  if (!tags?.length) return null
+  return (
+    <div className="flex flex-wrap gap-2 mb-6">
+      {tags.map((tag) => (
+        <span
+          key={tag}
+          className="inline-block px-2.5 py-0.5 text-xs leading-relaxed rounded
+                     text-[var(--rp-c-brand)] bg-[var(--rp-c-brand-tint)]
+                     whitespace-nowrap">
+          {tag}
+        </span>
+      ))}
+    </div>
+  )
+}