feat(fp): WP-14 — Storybook taxonomy reorg + Layers MDX

Retitle all 49 stories into a sidebar that makes the DDD seam visible:
Foundations (curriculum) -> Design System (Atoms/Molecules/Organisms/
Templates/Devtools, everything in shared/ui + shared/layout) -> Domein
(Registratie/Herregistratie/Auth/Brief, everything in a context's ui/).
Pin the order via storySort. Add layers.mdx explaining the split and
linking the enforcing eslint rules; document the story-title convention
in CLAUDE.md. Fix a stale "status banner" reference in atomic-design.mdx
left over from WP-13's upload-status-banner deletion.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CLAUDE.md

@@ -120,8 +120,12 @@ but the FE doesn't call them.
 Vitest. Co-locate `*.spec.ts` next to the unit. **Domain and pure logic must have a
 spec** (reducers, combinators, `visibleSteps`, parsers, boundary `parse*` adapters).
 Test the pure function directly — no Angular TestBed for domain. UI is exercised via
-Storybook stories (`*.stories.ts` co-located, titled `Layer/Name`, a11y addon on),
-not heavy component tests.
+Storybook stories (`*.stories.ts` co-located, a11y addon on), not heavy component tests.
+**Story titles mirror the sidebar's Design System/Domein split** (see
+`src/docs/layers.mdx`): a `shared/ui`/`shared/layout` component is titled
+`Design System/<Atoms|Molecules|Organisms|Templates|Devtools>/<Name>`; a component in a
+context's `ui/` is titled `Domein/<Context>/<Name>` — full stop, regardless of which
+atomic layer it is (a context organism doesn't get its own `Organisms/` bucket).
 
 ## Conventions