refactor: hide empty architecture card placeholder on mobile

- Added hidden md:flex classes to empty architecture card placeholder div
- Maintains desktop visibility while hiding on mobile for better responsive layout

src/pages/home/HomeArchitecture.tsx

@@ -97,7 +97,7 @@ export function HomeArchitecture() {
                     </div>
                   </div>
                 ) : (
-                  <div className="h-48 w-full flex items-center justify-center bg-transparent" />
+                  <div className="h-48 w-full items-center justify-center bg-transparent hidden md:flex" />
                 )}
 
                 <div className="px-8 pt-4 pb-6">