Add sample blog posts and fix rendering

- Add hello-world.md and second-post.md sample posts
- Fix index page: use set:html for links, add charset, import global.css
- Fix post page: add charset meta tag
- Fix remark plugin: use className array, handle leaf directives
- Update CSS: support left/right margin note classes

apps/blog/src/plugins/remark-aside.ts

@@ -3,12 +3,12 @@ import type { Root } from 'mdast';
 
 export default function remarkAside() {
   return (tree: Root) => {
-    visit(tree, 'textDirective', (node: any) => {
-      if (node.name !== 'aside') return;
+    visit(tree, ['textDirective', 'leafDirective'], (node: any) => {
+      if (node.name !== 'left' && node.name !== 'right') return;
 
       const data = node.data || (node.data = {});
       data.hName = 'span';
-      data.hProperties = { class: 'aside' };
+      data.hProperties = { className: [node.name] };
     });
   };
 }