Fix blog posts not appearing on site

The blog utility was looking for 'publishDate' field but .mdoc files
use 'date'. Updated the destructuring to read from 'date' field.

This fixes the missing blog posts on https://radio.org.tr/

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

src/utils/blog.ts

@@ -45,7 +45,8 @@ const getNormalizedPost = async (post: CollectionEntry<'post'>): Promise<Post> =
   const { Content, remarkPluginFrontmatter } = await render(post);
 
   const {
-    publishDate: rawPublishDate = new Date(),
+    date: rawPublishDate = new Date(),
+    publishDate: rawPublishDateAlt,
     updateDate: rawUpdateDate,
     title,
     excerpt,