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

package.json

@@ -15,6 +15,7 @@
   },
   "devDependencies": {
     "@eslint/js": "^9.39.4",
+    "@tailwindcss/postcss": "^4.3.0",
     "@types/node": "^22.8.1",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
@@ -23,6 +24,7 @@
     "prettier": "^3.8.2",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
+    "tailwindcss": "^4.3.0",
     "typescript-eslint": "^8.58.1"
   }
 }