feat: use xpier media library for uploads and markdown embeds

Store media:ID in post bodies instead of CDN URLs, and keep sablog attach tokens as a fallback.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Blog/Services/PostContentRenderer.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 
 namespace App\Blog\Services;
 
+use App\Blog\Support\MarkdownMediaEmbed;
 use App\Models\Post;
 use Illuminate\Support\Facades\Cache;
 use League\CommonMark\Environment\Environment;
@@ -36,11 +37,15 @@ class PostContentRenderer
      */
     public function render(Post $post): string
     {
+        $embed = app(MarkdownMediaEmbed::class);
+        $raw = (string) $post->content;
+
         $content = $post->content_format === 'markdown'
-            ? $this->toHtml($post->content)
-            : $post->content;
+            ? $this->toHtml($embed->expandMarkdown($raw))
+            : $raw;
 
         $html = $this->renderShortcodes($content, $post);
+        $html = $embed->hydrateHtml($html);
 
         // 插件钩子：付费内容过滤、AI 处理等
         $html = app(\App\Blog\Support\PluginManager::class)->applyFilters('post.rendered', $html, $post);