style: add responsive layout for mobile devices

Add media query to display cards in single column on mobile screens.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/index.tsx

@@ -85,6 +85,15 @@ export default function Index() {
             />
           ))}
         </div>
+
+        {/* 移动端响应式样式 */}
+        <style jsx>{`
+          @media (max-width: 768px) {
+            div[style*="gridTemplateColumns"] {
+              gridTemplateColumns: 1fr !important;
+            }
+          }
+        `}</style>
       </div>
     </div>
   );