Content pipeline overhaul: the site now builds itself from atoms

Rebuilt the content architecture from the ground up — log entries are now the only thing I write, and everything else composes from them. Thread pages render entries in expandable accordions. Project pages show a "How This Got Built" provenance section. The same MDX renders identically whether you're reading a standalone log entry, expanding it inside a thread timeline, or seeing it in a project's build history.

Along the way, fixed three production bugs that had been hiding: tables and headings had zero CSS styling site-wide, the ScoreBadge component showed "NaN%" on the Gemma 4 page because MDX doesn't pass numeric JSX props correctly, and the Edge Lab log entry was parented to the wrong thread. Cleaned up the content relationships, documented the atomic model, and built the publishing skill that generated this very entry.