feat(utils): add buildOfstedListBadge helper and fetchNationalAverages

- Add ofsted_framework field to School type
- Add OfstedListBadge interface and buildOfstedListBadge pure function to utils.ts
- Add fetchNationalAverages API function that calls GET /api/national-averages
- Add test suite for buildOfstedListBadge (all 6 new tests pass)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nextjs-app/__tests__/lib/utils.test.ts

@@ -8,6 +8,7 @@ import {
   calculateTrend,
   isValidPostcode,
   debounce,
+  buildOfstedListBadge,
 } from '@/lib/utils';
 
 describe('formatPercentage', () => {
@@ -102,3 +103,41 @@ describe('debounce', () => {
 
   jest.useRealTimers();
 });
+
+describe('buildOfstedListBadge', () => {
+  it('returns grade word + year for OEIF Outstanding', () => {
+    const badge = buildOfstedListBadge({ ofsted_grade: 1, ofsted_date: '2023-11-15', ofsted_framework: 'OEIF' });
+    expect(badge.label).toBe('Outstanding · 2023');
+    expect(badge.cssClass).toBe('ofsted1');
+  });
+
+  it('returns grade word for each OEIF grade', () => {
+    expect(buildOfstedListBadge({ ofsted_grade: 2, ofsted_date: '2022-05-01' }).label).toBe('Good · 2022');
+    expect(buildOfstedListBadge({ ofsted_grade: 3, ofsted_date: '2021-01-01' }).label).toBe('Req. Improvement · 2021');
+    expect(buildOfstedListBadge({ ofsted_grade: 4, ofsted_date: '2020-03-01' }).label).toBe('Inadequate · 2020');
+  });
+
+  it('returns grade word without year when date is missing', () => {
+    const badge = buildOfstedListBadge({ ofsted_grade: 2, ofsted_date: null });
+    expect(badge.label).toBe('Good');
+    expect(badge.cssClass).toBe('ofsted2');
+  });
+
+  it('returns Report Card badge when framework is ReportCard', () => {
+    const badge = buildOfstedListBadge({ ofsted_grade: null, ofsted_date: '2025-11-01', ofsted_framework: 'ReportCard' });
+    expect(badge.label).toBe('Report Card · 2025');
+    expect(badge.cssClass).toBe('ofstedRc');
+  });
+
+  it('returns pending badge when no grade and no ReportCard framework', () => {
+    const badge = buildOfstedListBadge({ ofsted_grade: null, ofsted_date: null, ofsted_framework: null });
+    expect(badge.label).toBe('Not yet inspected');
+    expect(badge.cssClass).toBe('ofstedPending');
+  });
+
+  it('returns pending badge when all fields are undefined', () => {
+    const badge = buildOfstedListBadge({});
+    expect(badge.label).toBe('Not yet inspected');
+    expect(badge.cssClass).toBe('ofstedPending');
+  });
+});