ads/chrome: banners on /search and /reading-list; wrap /contributor with site chrome

- /search and /reading-list already had Header + Footer; add a
    single in-content 728x90 banner at the bottom of each main column
    (gated on ADS_728X90.length > 0, hidden on mobile).

  - /contributor was a bare dashboard with sidebar + main, no site
    chrome at all. Wrap it in the standard Header + Footer; drop the
    inner sidebar/main wrapper from min-h-screen to a natural-height
    flex so the dashboard sits below the header instead of competing
    with it for full viewport. Header brings the site-wide 728x90
    leaderboard with it, so contributors see the same ad inventory
    as the public site without a second in-content banner cluttering
    the dashboard panes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/search/page.tsx

@@ -3,6 +3,8 @@ import Link from "next/link";
 import Header from "@/components/Header";
 import Footer from "@/components/Footer";
 import AppImage from "@/components/ui/AppImage";
+import AdImage from "@/components/AdImage";
+import { ADS_728X90, shuffle } from "@/lib/ads";
 import { searchLegacyArticles } from "@/lib/articles/legacy-source";
 
 export const revalidate = 60;
@@ -93,6 +95,13 @@ export default async function SearchPage({ searchParams }: SearchPageProps) {
             );
           })}
         </div>
+
+        {/* In-content 728x90 banner */}
+        {ADS_728X90.length > 0 && (
+          <div className="mt-10 hidden md:flex justify-center" aria-label="Advertisement">
+            <AdImage ad={shuffle(ADS_728X90)[0]} page="search" />
+          </div>
+        )}
       </main>
       <Footer />
     </div>