fix: joinedAt nullable in UserSchema, guard null in profile page

thoughts-frontend/app/users/[username]/page.tsx

@@ -188,7 +188,7 @@ export default async function ProfilePage({ params }: ProfilePageProps) {
               >
                 <Calendar className="h-4 w-4" />
                 <span>
-                  Joined {new Date(user.joinedAt).toLocaleDateString()}
+                  Joined {user.joinedAt ? new Date(user.joinedAt).toLocaleDateString() : "Unknown"}
                 </span>
               </div>
             </Card>

thoughts-frontend/app/users/all/page.tsx

@@ -28,7 +28,8 @@ export default async function AllUsersPage({
     );
   }
 
-  const { items, total, per_page } = usersData;\n  const perPage = per_page;
+  const { items, total, per_page } = usersData;
+  const perPage = per_page;
   const totalPages = Math.ceil(total / perPage);
 
   return (