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/shared/layout/page-shell/page-shell.stories.ts

@@ -5,7 +5,7 @@ import { PageShellComponent } from './page-shell.component';
 import { ButtonComponent } from '@shared/ui/button/button.component';
 
 const meta: Meta<PageShellComponent> = {
-  title: 'Templates/PageShell',
+  title: 'Design System/Templates/PageShell',
   component: PageShellComponent,
   decorators: [
     applicationConfig({ providers: [provideRouter([])] }),