feat(search): phases in the order a child meets them

The phase filter listed GIAS phases alphabetically, so "16 plus" and
"All-through" came before Nursery. /api/filters (and the result-scoped
list) now order them Nursery, Primary, Middle deemed primary, Middle
deemed secondary, Secondary, 16 plus, then All-through, which spans the
whole path. A phase GIAS adds later follows the known ones, A-Z.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

e2e/tests/journeys.spec.ts

@@ -286,6 +286,19 @@ test('the phase filter switches straight from secondary to primary', async ({ pa
   await expect(phase).toHaveValue('primary');
 });
 
+test('the phase filter lists phases in the order a child meets them', async ({ page }) => {
+  // They were alphabetical, so "16 plus" and "All-through" came before Nursery.
+  const childPath = ['Nursery', 'Primary', 'Middle deemed primary',
+    'Middle deemed secondary', 'Secondary', '16 plus', 'All-through'];
+  await page.goto('/?search=school');
+  const phase = page.getByRole('combobox', { name: 'Phase' });
+  await expect(phase).toBeVisible({ timeout: 15_000 });
+  const offered = (await phase.locator('option').allTextContents())
+    .filter((o) => childPath.includes(o));
+  expect(offered, 'no phase on offer').toContain('Primary');
+  expect(offered).toEqual(childPath.filter((p) => offered.includes(p)));
+});
+
 test('school type and gender switch straight to another value', async ({ page }) => {
   // Their options came from the result set, which the filter had already
   // narrowed, so with one value chosen it was the only one on offer.