refactor: streamline logout process by integrating next-auth's signOut and a dedicated server action for cookie management.

src/components/layout/CommonHeader.tsx

@@ -280,12 +280,6 @@ export function CommonHeader() {
                     <button
                       onClick={() => {
                         setShowProfileMenu(false);
-                        // Set logout flag FIRST so TokenSync and PresenceProvider
-                        // don't restore tokens during the logout navigation
-                        localStorage.setItem('isLoggingOut', 'true');
-                        localStorage.removeItem('accessToken');
-                        localStorage.removeItem('refreshToken');
-                        localStorage.removeItem('user');
                         window.location.href = '/logout';
                       }}
                       className="w-full flex items-center gap-3 px-4 py-3 hover:bg-black/5 transition-colors"