feat(comments): add character limit to comment markdown body

Add an optional `$limit` parameter to `CommentPresenter::markdownBody()`
that truncates the comment body before rendering Markdown. The comment
partial now passes a default limit of 250 characters, preventing long
comments from dominating the layout. Unit tests cover rendering with and
without a limit.

app/Models/Presenters/CommentPresenter.php

@@ -14,9 +14,15 @@ class CommentPresenter
         $this->comment = $comment;
     }
 
-    public function markdownBody()
+    public function markdownBody(?int $limit = null)
     {
-        return Str::of($this->comment->body)->markdown([
+        $body = $this->comment->body;
+
+        if ($limit !== null) {
+            $body = Str::limit($body, $limit);
+        }
+
+        return Str::of($body)->markdown([
             'html_input' => 'strip',
         ]);
     }