feat(blog) add CMS, render blog posts list

- use GitHub repo as cms, read idx.json
- blog posts list

app/blog/layout.tsx

@@ -0,0 +1,15 @@
+import React from 'react';
+
+function Layout({
+    children
+}: {
+    children: React.ReactNode;
+}) {
+    return (
+        <div className={ 'flex items-stretch justify-center' }>
+            { children }
+        </div>
+    );
+}
+
+export default Layout;