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>

src/app/registratie/ui/registration-summary/registration-summary.stories.ts

@@ -11,7 +11,7 @@ const base = {
 } satisfies Omit<Registration, 'status'>;
 
 const meta: Meta<RegistrationSummaryComponent> = {
-  title: 'Organisms/Registration Summary',
+  title: 'Domein/Registratie/Registration Summary',
   component: RegistrationSummaryComponent,
 };
 export default meta;