fix(youtube-facade): use is_singular() instead of is_single()

Changed condition from is_single() to is_singular() to ensure
YouTube facade assets load on all singular content types.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Public/YoutubeFacade/Infrastructure/Wordpress/YoutubeFacadeHooksRegistrar.php

@@ -44,8 +44,9 @@ final class YoutubeFacadeHooksRegistrar
      */
     public function enqueueAssets(): void
     {
-        // Only on single posts where videos might appear
-        if (!is_single()) {
+        // Only on singular content (posts, pages, custom post types)
+        // Changed from is_single() to is_singular() to cover all content types
+        if (!is_singular()) {
             return;
         }