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>

resources/views/articles/show.blade.php

@@ -1,7 +1,18 @@
 @extends('master')
 
-@section('title'){{ strip_tags($article->title) }} « @stop
+@section('title'){{ $article->published ? '' : '[Draft] ' }}{{ strip_tags($article->title) }} « @stop
+
+@if (! $article->published)
+    @push('head')
+        <meta name="robots" content="noindex, nofollow">
+    @endpush
+@endif
 
 @section('content')
+    @unless ($article->published)
+        <aside class="draft-notice" role="note">
+            <strong>Draft</strong> — this post hasn’t been published yet. It isn’t listed on the site or in feeds, so only people with this link can see it.
+        </aside>
+    @endunless
     @include('templates.article', ['article' => $article])
 @stop