fix(site): work around Astro SSR false "Invalid hook call" warnings (#600)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

site/src/components/docs/PreferenceUpdater.tsx

@@ -24,5 +24,7 @@ export function PreferenceUpdater({ currentFramework }: PreferenceUpdaterProps)
     styleStore.set(style);
   }, [currentFramework]);
 
-  return null;
+  // Workaround: Astro SSR logs false "Invalid hook call" when a React
+  // component with hooks returns null. See withastro/astro#12283.
+  return <></>;
 }