feat(auth): refactor sign-out functionality and update import paths

frontend/app/Navigation.tsx

@@ -1,5 +1,6 @@
 import Link from 'next/link';
-import { auth, signOut } from '../auth';
+import { auth } from '../auth';
+import { signOutAction } from './actions/auth-actions';
 
 const linkStyle: React.CSSProperties = {
   padding: '0.5rem 0.75rem',
@@ -41,12 +42,7 @@ export default async function Navigation() {
           <span style={{ fontSize: '0.9rem', color: '#555' }}>
             👤 {session.user.name}
           </span>
-          <form
-            action={async () => {
-              'use server';
-              await signOut({ redirectTo: '/login' });
-            }}
-          >
+          <form action={signOutAction}>
             <button
               type="submit"
               style={{