fix(places): submit and link the phase variants

/schools/[place]/[phase] shipped as routes but reached nothing. The sitemap
emitted one URL per registry entry and the registry had no phase dimension, so
~950 pages were absent from every sitemap — and PlaceView did not link them
either, leaving them reachable by nothing at all.

That is the query shape the baseline actually showed: 'primary schools in
beccles', 'secondary schools in brentwood'. Publishing the routes without a
path in meant building for the demand and then hiding from it.

Place now carries phase_urns so the per-phase threshold can be applied without
re-querying, the sitemap emits a variant wherever a phase clears the threshold
on its own, and the API exposes the qualifying phases so the place page links
only variants that exist. Outcodes are excluded: nobody searches 'primary
schools in SW11' and those routes do not exist.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

e2e/tests/journeys.spec.ts

@@ -1842,3 +1842,29 @@ test('a place page states the local average against England', async ({ page }) =
   await page.goto(`/schools/${place.slug}`);
   await expect(page.getByTestId('local-vs-england')).toContainText(/across England/i);
 });
+
+test('a place page links its phase variants, and they resolve', async ({ page }) => {
+  // "primary schools in beccles" is the query shape the baseline showed. The
+  // first cut submitted only the bare place URL and linked nothing, leaving
+  // ~950 variant pages reachable by nothing at all.
+  const res = await page.request.get('/api/places');
+  const { places } = await res.json();
+  const town = places.find((p: { kind: string }) => p.kind === 'town');
+  expect(town).toBeTruthy();
+
+  const detail = await (await page.request.get(`/api/places/town/${town.slug}`)).json();
+  test.skip(!(detail.place.phases ?? []).length, 'no phase clears the threshold here');
+
+  await page.goto(`/schools/${town.slug}`);
+  const phase = detail.place.phases[0];
+  const link = page.locator(`a[href="/schools/${town.slug}/${phase}"]`).first();
+  await expect(link).toBeVisible();
+
+  await link.click();
+  await expect(page.locator('h1')).toContainText(new RegExp(`${phase} schools in`, 'i'));
+});
+
+test('phase variants are submitted in the places sitemap', async ({ page }) => {
+  const xml = await (await page.request.get('/sitemaps/places-1.xml')).text();
+  expect(xml).toMatch(/\/schools\/[a-z0-9-]+\/primary</);
+});