Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/app/admin/ads/page.tsx

@@ -18,9 +18,7 @@ export default async function AdminAds() {
     ads = [];
   }
 
-  const latest = ads[0]?.createdAt
-    ? ads[0].createdAt.toISOString().slice(0, 10)
-    : "—";
+  const latest = ads[0]?.createdAt ? ads[0].createdAt.toISOString().slice(0, 10) : "—";
 
   return (
     <main>