docs(backlog): add Phase 8 — platform/DX/showcase (WP-37..46)

New phase from the 5-item analysis: linked showcase snippets + animations,
runnable scaffolding generators (pages/wizards/context/SSP), dependency graph +
declarative boundaries, PII hardening (branded Bsn VO + masked-value atom +
persisted no-PII audit) doubling as a privacy showcase, and Vitest coverage.
Goal: both a teaching showcase and a production starter template. Sequenced with
priorities + dependencies in the README.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/project/backlog/WP-39-showcase-snippets-animations.md

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+# WP-39 — Showcase: linked code snippets + teaching animations
+
+Status: todo
+Phase: 8 — platform/DX/showcase
+Priority: P1
+
+## Why
+
+The `/concepts` showcase shows live components, but its code snippets are hand-authored
+`innerHTML` strings with manual highlighting — they drift from the real code. And the animation
+toolkit (`withViewTransitions`, native `animate.enter/leave`, reduced-motion-safe keyframes in
+`styles.scss`) is proven in dashboard/upload but unused for teaching motion.
+
+## Decisions
+
+- **Anti-drift snippets:** load _real_ source excerpts via Vite `?raw` imports with `// #region name`
+  markers + a tiny pure extractor; render with lightweight highlighting. No more `innerHTML` literals.
+- On the Storybook/MDX side, use `<Source>`/Canvas "show code" consistently (extend beyond the
+  current 4 of 14 pages).
+- **Reuse** the existing motion toolkit (no new animation lib): `animate.enter/leave` on the
+  fold/union demos + a "step through `reduce`" animation for the TEA loop; keep reduced-motion-safe.
+
+## Files
+
+- `src/app/showcase/concepts.page.ts` — replace `innerHTML` snippets with `?raw`+region excerpts;
+  apply animations.
+- New tiny extractor util (pure) + spec (region slicing).
+- `src/docs/machines.mdx`, `fp-in-ui.mdx`, `remote-data.mdx` — reference the live linked snippets.
+
+## Acceptance criteria
+
+- [ ] Every showcase snippet is sourced from a real file (edit the source → snippet updates); none
+      hand-copied.
+- [ ] The TEA/fold demos animate (reduced-motion respected); no new animation dependency.
+- [ ] Storybook a11y stays green; `npm run ci` green.