Resolve the language setting persistence issue

- Move i18n initialization to async function
- Sync i18n with settings store language
- Add Root component for i18n loading state
- Convert i18n.js to TypeScript

lightrag_webui/src/components/Root.tsx

@@ -0,0 +1,24 @@
+import { StrictMode, useEffect, useState } from 'react'
+import { initializeI18n } from '@/i18n'
+import App from '@/App'
+
+export const Root = () => {
+  const [isI18nInitialized, setIsI18nInitialized] = useState(false)
+
+  useEffect(() => {
+    // Initialize i18n immediately with persisted language
+    initializeI18n().then(() => {
+      setIsI18nInitialized(true)
+    })
+  }, [])
+
+  if (!isI18nInitialized) {
+    return null // or a loading spinner
+  }
+
+  return (
+    <StrictMode>
+      <App />
+    </StrictMode>
+  )
+}