Move the active-app reference into the book tree as the arts composition root,
the App-side analogue of active-uix.md:
- new docs/architecture/active-app.md (frontmatter + fixed relative paths); the
dated Spanish "Handoff 2026-05-13" heading becomes a timeless "Quick start".
- extract that Handoff block verbatim (ES) to docs/process/handoffs-2026-05.md,
alongside the other extracted arts/uix handoffs.
- stub src/arts/active-app/README.md pointing at the chapter (active-uix pattern).
- wire the chapter into the docs/README.md E1 map.
docs:check 0 errors (11 pre-existing warnings unrelated).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
