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/ui/alert/alert.stories.ts

@@ -2,7 +2,7 @@ import type { Meta, StoryObj } from '@storybook/angular';
 import { AlertComponent } from './alert.component';
 
 const meta: Meta<AlertComponent> = {
-  title: 'Atoms/Alert',
+  title: 'Design System/Atoms/Alert',
   component: AlertComponent,
   render: (args) => ({
     props: args,