tasks

Migrate Participant Stacks from Markdown to Turso with DB→Markdown Materialization

Stacks (current / aspirational / abandoned) live today in src/content/participants/<handle>.md and persist via GitHub App commits on every save — the same pattern the polling blueprint v2 §8.1 explicitly retired for time-sensitive data because of commit-history pollution, PEM brittleness, and concurrent-edit fragility. This task moves stacks to Astro DB on Turso as the authoritative store, with a periodic snapshot back to markdown so the build-in-public visibility stays intact. Generalizes the same materialization motion polling already uses (v2 §9), bringing two surfaces under one principled pattern.