Move reactable demo from content/posts/ to content/demos/ so it
doesn't appear in the posts list. Add demo pages for:
- Mermaid: flowchart, sequence, and state diagrams via code blocks
- KaTeX: inline and display math via the math partial
- Shortcodes: toc, rawhtml, youtube, vimeo
All demos are draft: true and in a dedicated section, so they
build with hugo --buildDrafts but are never published.
Also widen Makefile RMD_SOURCES glob to include content/demos/.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
70bf848fa3