Hide draft articles from the front page and mark drafts when viewed directly

Add an Article::published() scope and use it on the front page (which
previously showed drafts), the /blog listing and the feeds. Draft
articles are still reachable at their URL, but now show a draft notice,
a "[Draft]" title prefix and a noindex robots meta tag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/Http/Controllers/ArticlesController.php

@@ -17,7 +17,7 @@ class ArticlesController extends Controller
      */
     public function index(?int $year = null, ?int $month = null): View
     {
-        $articles = Article::where('published', '1')
+        $articles = Article::published()
             ->date($year, $month)
             ->orderBy('updated_at', 'desc')
             ->simplePaginate(5);