fix: og-image => thumbnail

renamed og-image to thumbnail for external blog posts

app/pages/blog/index.vue

@@ -65,7 +65,7 @@ const externalPosts = computed<BlogCard[]>(() => externalPostsRaw.value?.flatMap
   return externalBlog.posts.map(post => ({
     title: post.title,
     description: post.excerpt,
-    image: post['og-image'],
+    image: post.thumbnail,
     date: post.date,
     link: post.url,
     category: 'extern',