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>

tests/Feature/FrontPageTest.php

@@ -31,4 +31,15 @@ class FrontPageTest extends TestCase
             ->assertSee('https://example.com')
             ->assertSee('Like 1');
     }
+
+    #[Test]
+    public function front_page_does_not_show_draft_articles(): void
+    {
+        Article::factory()->create(['title' => 'Published Article']);
+        Article::factory()->create(['title' => 'Draft Article', 'published' => 0]);
+
+        $this->get('/')
+            ->assertSee('Published Article')
+            ->assertDontSee('Draft Article');
+    }
 }