feat(blog) add CMS, render blog posts list

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

app/blog/fetch_posts.ts

@@ -0,0 +1,19 @@
+import { Result } from '@/app/public/type/Result';
+
+export default async function fetch_posts(url: string): Promise<Result<JSON[], Error>> {
+    const response = await fetch(`${ url }/posts/idx.json`);
+    if (!response.ok) {
+        return {
+            ok: false,
+            error: new Error(response.statusText)
+        };
+    }
+    const res = await response.json();
+    const posts = res['idx'].filter((posts: { type: string }) => posts.type === 'md');
+    return {
+        ok: true,
+        value: posts
+    };
+}
+
+