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.

tests/Unit/CommentPresenterTest.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Tests\Unit;
+
+use App\Models\Comment;
+use Tests\TestCase;
+
+class CommentPresenterTest extends TestCase
+{
+    public function test_markdown_body_renders_full_comment_without_limit(): void
+    {
+        $comment = new Comment(['body' => 'Hello **world**']);
+
+        $result = (string) $comment->presenter()->markdownBody();
+
+        $this->assertStringContainsString('Hello', $result);
+        $this->assertStringContainsString('world', $result);
+    }
+
+    public function test_markdown_body_is_truncated_when_limit_is_provided(): void
+    {
+        $body = str_repeat('a very long comment. ', 50);
+        $comment = new Comment(['body' => $body]);
+
+        $result = (string) $comment->presenter()->markdownBody(40);
+
+        $this->assertLessThan(strlen($body), strlen($result));
+        $this->assertStringContainsString('...', $result);
+    }
+
+    public function test_markdown_body_is_not_truncated_when_body_is_shorter_than_limit(): void
+    {
+        $comment = new Comment(['body' => 'Short']);
+
+        $result = (string) $comment->presenter()->markdownBody(100);
+
+        $this->assertStringContainsString('Short', $result);
+        $this->assertStringNotContainsString('...', $result);
+    }
+}