feat(destinations): the post-16 section, replacing the placeholder

The 'Post-16 destination data coming soon' note is deleted rather than
reworded: for a school with no sixth form the truthful statement is that
the question does not apply, and a placeholder there implies something is
missing. hasSixthForm and .sixthFormNote go with it — nothing else used them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BvdDKvFFSZuMVDH5fEyTob

nextjs-app/__tests__/components/Post16DestinationsSection.test.tsx

@@ -0,0 +1,45 @@
+import { render, screen } from '@testing-library/react';
+import { Post16DestinationsSection } from '@/components/school/Post16DestinationsSection';
+import type { DestinationPhase } from '@/lib/types';
+
+const phase: DestinationPhase = {
+  cohort_year: '2022/23',
+  groups: {
+    all: {
+      cohort: 96,
+      categories: [
+        { category: 'higher_education', pupils: 56, percentage: 58.3, status: 'published' },
+        { category: 'further_education', pupils: 12, percentage: 12.5, status: 'published' },
+        { category: 'apprenticeship', pupils: 9, percentage: 9.4, status: 'published' },
+        { category: 'employment', pupils: 13, percentage: 13.5, status: 'published' },
+        { category: 'not_sustained', pupils: 6, percentage: 6.3, status: 'published' },
+      ],
+      aggregates: {},
+    },
+  },
+};
+
+describe('Post16DestinationsSection', () => {
+  it('names the Year 13 cohort, not Year 11', () => {
+    const { container } = render(<Post16DestinationsSection destinations={phase} />);
+    expect(container.textContent).toMatch(/Year 13/);
+    expect(container.textContent).not.toMatch(/Year 11/);
+  });
+
+  it('reports higher education destinations', () => {
+    render(<Post16DestinationsSection destinations={phase} />);
+    expect(screen.getByText(/UK higher education/i)).toBeInTheDocument();
+  });
+
+  it('uses its own anchor so the nav does not collide with After Year 11', () => {
+    const { container } = render(<Post16DestinationsSection destinations={phase} />);
+    expect(container.querySelector('#post16-destinations')).toBeTruthy();
+    expect(container.querySelector('#destinations')).toBeNull();
+  });
+
+  it('renders nothing when no group carries categories', () => {
+    const empty: DestinationPhase = { cohort_year: '2022/23', groups: {} };
+    const { container } = render(<Post16DestinationsSection destinations={empty} />);
+    expect(container.firstChild).toBeNull();
+  });
+});