Integrate AuthInitializer component to restore authentication state on app load and enhance User type to align with OpenAPI spec.

frontend/src/app/providers.tsx

@@ -3,6 +3,7 @@
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { ReactQueryDevtools } from '@tanstack/react-query-devtools';
 import { useState } from 'react';
+import { AuthInitializer } from '@/components/auth';
 
 export function Providers({ children }: { children: React.ReactNode }) {
   const [queryClient] = useState(
@@ -23,6 +24,7 @@ export function Providers({ children }: { children: React.ReactNode }) {
 
   return (
     <QueryClientProvider client={queryClient}>
+      <AuthInitializer />
       {children}
       <ReactQueryDevtools initialIsOpen={false} />
     </QueryClientProvider>