Converts existing server-side JSON blog posts to Markdown format with
YAML frontmatter so they appear in TinaCloud admin and are managed via git.
Also fixes sync-blog.mjs parseFrontmatter to support multi-line YAML lists
(TinaCMS writes hashtags as multi-line list items).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
