Update existing draft articles instead of erroring on a repeat Micropub post

If a Micropub h-entry post's title matches an existing article that's
still a draft, update that article in place rather than trying to
insert a duplicate. If it matches one that's already published,
reject the request with a clear error instead of silently colliding.

Also set includeTrashed on Article's slug config as a safety net: this
model soft-deletes, and Sluggable's uniqueness check ignores trashed
rows by default, so a previously-deleted article's title could crash
new inserts with a raw unique constraint violation (this is exactly
what surfaced in Flare as a UniqueConstraintViolationException on
articles_titleurl_unique once the prior swallowed-exception fix
shipped).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/Services/ArticleService.php

@@ -8,12 +8,29 @@ use App\Models\Article;
 
 class ArticleService
 {
+    /**
+     * @throws \InvalidArgumentException if a published article already has this title
+     */
     public function create(array $data): Article
     {
-        return Article::create([
+        $attributes = [
             'title' => $data['name'],
             'main' => $data['content'],
             'published' => ($data['post-status'] ?? null) !== 'draft',
-        ]);
+        ];
+
+        $existing = Article::where('title', $data['name'])->first();
+
+        if ($existing !== null) {
+            if ($existing->published) {
+                throw new \InvalidArgumentException("An article titled \"{$data['name']}\" has already been published");
+            }
+
+            $existing->update($attributes);
+
+            return $existing;
+        }
+
+        return Article::create($attributes);
     }
 }