restore YAML frontmatter

next.config.ts

@@ -129,6 +129,8 @@ const withBundleAnalyzer = createBundleAnalyzer({
 const withMDX = createMDX({
   options: {
     remarkPlugins: [
+      mdxPlugins.remarkFrontmatter,
+      mdxPlugins.remarkMdxFrontmatter,
       [mdxPlugins.remarkGfm, { singleTilde: false }],
       [
         mdxPlugins.remarkSmartypants,