fix(web): fix doubled section prefix in doc links (404 on click)

Home page, search results, and doc page Related links all
generated hrefs as /${section}/${slug} but slug already
includes the section prefix (e.g. 'docs/websocket/contract'),
producing doubled URLs like /docs/docs/websocket/contract → 404.
Fix: href={`/${d.slug}`} everywhere.

apps/web/app/[section]/[...slug]/page.tsx

@@ -45,7 +45,7 @@ export default async function DocPage({
             {related.map((r) => (
               <li key={r.slug}>
                 <Link
-                  href={`/${r.section}/${r.slug}`}
+                  href={`/${r.slug}`}
                   className="hover:underline"
                 >
                   {r.title}