feat(fp): WP-15 — missing stories: shell + brief components

Add the 7 stories CLAUDE.md's testing rule ("UI is exercised via Storybook
stories") was missing: shared/layout/shell (Design System/Templates/Shell)
and all six previously-unstoried brief components (passage-picker,
rejection-comments, diagnostics-panel, letter-block, letter-preview,
letter-section — Domein/Brief/*), each with a default state plus the
meaningful variants (locked/editable, findings/clean, show/entry, etc).
Every *.component.ts in the repo now has a co-located story; *.page.ts
files stay unstoried, matching the existing norm.

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

src/app/brief/ui/rejection-comments/rejection-comments.stories.ts

@@ -0,0 +1,16 @@
+import type { Meta, StoryObj } from '@storybook/angular';
+import { RejectionCommentsComponent } from './rejection-comments.component';
+
+const meta: Meta<RejectionCommentsComponent> = {
+  title: 'Domein/Brief/Rejection Comments',
+  component: RejectionCommentsComponent,
+  args: { reject: () => {} },
+};
+export default meta;
+type Story = StoryObj<RejectionCommentsComponent>;
+
+export const Show: Story = {
+  args: { mode: 'show', comments: 'Graag de aanhef formeler.' },
+};
+export const Entry: Story = { args: { mode: 'entry' } };
+export const EntryBusy: Story = { args: { mode: 'entry', busy: true } };