Align all elements on the article page to have consistent horizontal spacing

Constrain the max-width of the prediction markets section to match the article body by applying `max-w-4xl mx-auto` to the section element in `client/src/pages/Article.tsx`.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 0fb68265-c270-4198-9584-3d9be9bddb41
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/3df548ff-50ae-432f-9be4-25d34eccc983/0fb68265-c270-4198-9584-3d9be9bddb41/rOJiPGe

client/src/pages/Article.tsx

@@ -216,7 +216,7 @@ export default function Article() {
         </article>
 
         {/* Prediction Markets Section */}
-        <section>
+        <section className="max-w-4xl mx-auto">
           <div className="flex items-center space-x-3 mb-6">
             <TrendingUp className="h-6 w-6 text-primary" />
             <h2 className="text-2xl font-bold">관련 예측시장</h2>