Wire MediaEmbedExtension into Document::renderMarkdown

The extension registers a DocumentParsedEvent listener that walks the
AST, finds Image nodes whose URLs match media patterns (via
MediaUrlResolver), and replaces them with MediaEmbedNode instances
containing the appropriate <video>/<audio>/<iframe> markup.

A custom MediaEmbedNode + MediaEmbedNodeRenderer pair bypasses the
html_input filter (which would strip raw HTML when set to 'strip'),
allowing programmatically generated embed HTML to pass through safely
while user-authored raw HTML remains stripped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/tests/Unit/Markdown/MediaEmbedExtensionTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Tests\Unit\Markdown;
+
+use App\Models\Document;
+use Tests\TestCase;
+
+class MediaEmbedExtensionTest extends TestCase
+{
+    public function test_normal_image_still_renders_as_img(): void
+    {
+        $html = Document::renderMarkdown('![alt](/photo.png)');
+        $this->assertStringContainsString('<img', $html);
+        $this->assertStringContainsString('src="/photo.png"', $html);
+    }
+
+    public function test_video_url_renders_as_video_tag(): void
+    {
+        $html = Document::renderMarkdown('![](/demo.mp4)');
+        $this->assertStringContainsString('<video', $html);
+        $this->assertStringContainsString('src="/demo.mp4"', $html);
+        $this->assertStringNotContainsString('<img', $html);
+    }
+
+    public function test_youtube_url_renders_as_iframe(): void
+    {
+        $html = Document::renderMarkdown('![](https://youtu.be/dQw4w9WgXcQ)');
+        $this->assertStringContainsString('<iframe', $html);
+        $this->assertStringContainsString('youtube-nocookie.com', $html);
+    }
+
+    public function test_vimeo_url_renders_as_iframe(): void
+    {
+        $html = Document::renderMarkdown('![](https://vimeo.com/123456789)');
+        $this->assertStringContainsString('<iframe', $html);
+        $this->assertStringContainsString('player.vimeo.com', $html);
+    }
+}