Add an advertisement card to the blog post category page

Integrate `ArticleCardAd` component into the category page's article grid to display an advertisement between posts.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 413891e8-d784-4bea-b9f5-91a5a68316b4
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Replit-Commit-Event-Id: 280e79de-a056-4133-85e8-89539a552ee8
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client/src/pages/category.tsx

@@ -8,6 +8,7 @@ import { Button } from "@/components/ui/button";
 import { Skeleton } from "@/components/ui/skeleton";
 import Header from "@/components/header";
 import Footer from "@/components/footer";
+import { ArticleCardAd } from "@/components/adsense";
 
 export default function CategoryPage() {
   const { category } = useParams<{ category: string }>();
@@ -46,10 +47,11 @@ export default function CategoryPage() {
           </div>
         ) : articles && articles.length > 0 ? (
           <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
-            {articles.map((article) => (
+            {articles.flatMap((article, index) => {
+              const items = [
                 <Link key={article.id} href={`/article/${article.slug}`}>
                   <article
-                  className="group cursor-pointer bg-card rounded-md border border-card-border transition-all duration-300"
+                    className="group cursor-pointer bg-card rounded-md border border-card-border transition-all duration-300 h-full"
                     data-testid={`card-article-${article.id}`}
                   >
                     <div className="relative rounded-t-md">
@@ -85,8 +87,13 @@ export default function CategoryPage() {
                       </div>
                     </div>
                   </article>
-              </Link>
-            ))}
+                </Link>,
+              ];
+              if (index === 2) {
+                items.push(<ArticleCardAd key="ad-cat-1" />);
+              }
+              return items;
+            })}
           </div>
         ) : (
           <div className="text-center py-16">