Collapse the eight Mikado scaffolding cards (+ goal card) into one
user-facing how-to, docs/how-to/self-update.md: what self-update is and
how to enable it. The per-card breakdown was build-time scaffolding, not
documentation. Keeps the changelog fragment; updates the how-to index.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
