feat(showcase): WP-39 — linked code snippets + teaching animations

Anti-drift snippets: `?raw` isn't supported by Angular's esbuild build, so real code
is exposed via // #region showcase:<name> markers in source (registration/remote-data/
postcode/change-request.machine/intake.machine) → scripts/gen-snippets.mjs → committed
snippets.generated.ts, with a CI drift gate so the shown code is the shipped code. The
/concepts page renders the 5 real snippets (union/fold/parse/machine/steps) with a source
caption + a tiny dependency-free highlightTs (+spec); deliberately-wrong illustrations stay
authored. Teaching motion: active state node pops on transition + parse result animates in
(existing reduced-motion-safe toolkit). Generated file prettier-ignored (like api-client).

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

.prettierignore

@@ -10,6 +10,7 @@ package-lock.json
 # Generated — owned by their generators, not prettier
 documentation.json
 src/app/shared/infrastructure/api-client.ts
+src/app/showcase/snippets.generated.ts
 
 # Vendored design system (CIBG Huisstijl)
 public/cibg-huisstijl/