fix: show author description on magazine article page

Add description field to ARTICLE_BY_SLUG_QUERY and render it in the
author bio card below the name.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/lib/services.ts

@@ -296,6 +296,7 @@ const ARTICLE_BY_SLUG_QUERY = gql`
         artist_name
         slug
         avatar
+        description
       }
     }
   }