Add advertisements to fill empty spaces on the homepage

Injects `ArticleCardAd` components into rows that do not contain widgets, ensuring a consistent four-column layout on the home page. Updates image URLs in `gallery-data.json`.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 1f7e7e89-a520-4970-9645-37daadc466dc
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 4f807297-9291-4e24-9592-e66ee067829b
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/f209e72a-0939-48fa-84fc-57854de71967/1f7e7e89-a520-4970-9645-37daadc466dc/NJvOVoB
Replit-Helium-Checkpoint-Created: true

client/src/pages/home.tsx

@@ -548,6 +548,16 @@ export default function Home() {
       }
     }
 
+    let adCount = 0;
+    const totalRows = items.length / 4;
+    for (let r = 0; r < totalRows; r++) {
+      const rowStart = r * 4;
+      const hasWidget = items.slice(rowStart, rowStart + 4).some((it) => it.type === "widget");
+      if (!hasWidget) {
+        items[rowStart + 3] = { type: "ad", key: `ad-row-${adCount++}` };
+      }
+    }
+
     return items;
   }, [shuffled, widgets]);
 
@@ -656,9 +666,11 @@ export default function Home() {
               {row.map((item) =>
                 item.type === "widget"
                   ? <div key={item.key}>{item.widget!.el}</div>
-                  : item.article
-                    ? <MediumCard key={item.key} article={item.article} focalPoints={focalPoints} />
-                    : null
+                  : item.type === "ad"
+                    ? <div key={item.key} className="h-full" data-testid={`ad-grid-${item.key}`}><ArticleCardAd /></div>
+                    : item.article
+                      ? <MediumCard key={item.key} article={item.article} focalPoints={focalPoints} />
+                      : null
               )}
               {ri === gridRows.length - 1 && widePickedArticles.length > 0 && (
                 <div className="sm:col-span-2 lg:col-span-4 grid grid-cols-1 sm:grid-cols-2 gap-4">