Markdown sources

One file per item, with YAML front matter. 211 files: 193 carry the article text, the other 18 are audio or video and hold metadata only, since the archive links to those rather than transcribing them. The short posts are not here — they have no Markdown source and come from social-posts.json. For bulk use prefer index.json (metadata for every record, full text where available) or all.md.