Create bookmarks.yaml data file with sample entries and update
index.astro to import, parse, and display bookmarks with format
DD/MM/YY Site Name (domain.com)
- 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
