feat(i18n): add internationalization support with astro-i18next

- Add astro-i18next package for i18n support
- Create LanguageSwitcher component with English and Chinese options
- Add i18n guide documentation
- Update .gitignore and package.json

package.json

@@ -23,6 +23,7 @@
     "@types/react-dom": "^19.0.4",
     "aos": "^2.3.4",
     "astro": "^5.5.3",
+    "astro-i18next": "1.0.0-beta.21",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "framer-motion": "^12.5.0",