feat(i18n): add internationalization support with i18next

- Add i18next and related dependencies for internationalization
- Implement language switcher component with English and Chinese support
- Create translation files for English and Chinese locales
- Update login and home pages to use translations
- Configure i18n initialization with language detection
- Add dayjs locale synchronization with i18n language changes
- Update tsconfig and eslint to ignore new locales directory
- Remove unused App.css and simplify index.css
- Update npmrc with mirror configuration

tsconfig.json

@@ -3,5 +3,6 @@
   "references": [
     { "path": "./tsconfig.app.json" },
     { "path": "./tsconfig.node.json" }
-  ]
+  ],
+  "exclude": ["rag_web_core"]
 }