chore: Update auth files for NextAuth v5 compatibility

Breaking changes for NextAuth v5:
- Updated route.ts to use NextAuthConfig and new export pattern
- Changed getServerSession import to use auth from config
- Updated types and session handling for NextAuth v5
- Maintained backward compatibility with existing auth flow

frontend/lib/auth.ts

@@ -1,8 +1,8 @@
-import { getServerSession } from 'next-auth'
+import { auth } from '@/app/api/auth/[...nextauth]/route'
 import { redirect } from 'next/navigation'
 
 export async function requireAuth() {
-  const session = await getServerSession()
+  const session = await auth()
 
   if (!session || !session.user) {
     redirect('/auth/signin')