feat(admissions): add the cut-off history, map and postcode check

Completes the last-distance-offered feature against the mockup: the
year-by-year record, the same numbers drawn over real streets, and the
reader's own address measured against them.

Serving the history
  The first cut deliberately served only the latest year, because a plain
  series would draw a trend line straight through gaps that are absences of
  publication, not of a cut-off. That reasoning is answered rather than
  abandoned: cutoffYearRows classifies every year in the span, and the chart
  breaks the line rather than interpolating across it.

  A missing year is not one fact but three. It may be unpublished; it may be
  a year the school was not oversubscribed; or there may be no record at all.
  Collapsing them into "no data" throws away the reassuring case and hides
  the important caveat, so each is stated in words in the table.

  The claim is held to what the data supports. fact_admissions.oversubscribed
  compares FIRST PREFERENCES against places, which does not establish that
  every applicant was offered one — so the copy says "places available on
  first preferences" and a test asserts the stronger claim never appears.

The trend summary is not a verdict
  It names both endpoints and their years and lets the reader conclude. It is
  withheld below four published points, and a swing under a tenth of the
  earlier figure is reported as "broadly the same" rather than dressed up as
  a direction.

The postcode check
  This is the only place on the site that answers a question about a family
  rather than a school, so most of the care went into what it refuses to say.
  postcodes.io returns a centroid covering roughly fifteen addresses, which
  against a 500 m cut-off is a fifth of the whole distance — so a margin
  inside 100 m returns "too close to call" rather than a place a family does
  not have. Unpublished years count as unknown, never as a pass. The limits
  are stated before the check is used, not revealed with the answer.

  The postcode is geocoded in the browser and never stored.

Both templates
  Banded and selective secondaries are exactly where this matters most, so
  the detail is shared. The primary page gives it a third tab; the secondary
  page is one flat panel by design and renders it inline.

Absence is explained rather than reported. A selective school's missing
figure is explained by how it admits; a consistently undersubscribed school
reads as good news.

Also makes the batch loader's test double honour ORDER BY. It was a no-op,
so "latest row per URN" was really "first row in the fixture" and the test
would have passed with the sort reversed or removed.

Verified: 214 frontend tests, 54 backend, 45/53 e2e green against staging
(the 8 cut-off journeys skip until the DAG runs). Rendered offline against
the real compiled CSS in both themes and at 390px; every new surface clears
WCAG AA, measured on composited pixels.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WDvkyqqHABm4bmth2kjAxE

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

@@ -8,7 +8,7 @@
  * sentence appears only when it is actually true.
  */
 
-import { screen } from '@testing-library/react';
+import { screen, fireEvent } from '@testing-library/react';
 import { renderSchoolDetail, renderSecondarySchoolDetail } from '../support/renderSchoolDetail';
 import { primaryFixture, secondaryFixture } from '../support/schoolFixtures';
 import type { SchoolAdmissionDistance } from '@/lib/types';
@@ -88,3 +88,122 @@ describe('secondary detail page', () => {
     expect(screen.getByText(/has not published a cut-off distance/)).toBeInTheDocument();
   });
 });
+
+// ── The Distance view ──────────────────────────────────────────────────
+
+const history = (pts: [number, number][]): SchoolAdmissionDistance[] =>
+  pts.map(([year, distance_m]) => ({
+    year, distance_m, route_count: 1, la_name: 'Camden', distance_unit_raw: 'miles',
+  }));
+
+describe('primary Distance view', () => {
+  it('appears once there are two or more published years', () => {
+    renderSchoolDetail({
+      ...primaryFixture,
+      admissionDistance: cutoff({ distance_m: 700, year: 2024 }),
+      admissionDistanceHistory: history([[2021, 1000], [2022, 900], [2023, 800], [2024, 700]]),
+    });
+
+    expect(screen.getByRole('button', { name: 'Distance' })).toBeInTheDocument();
+  });
+
+  it('stays hidden on a single published year', () => {
+    // One point is a fact, not a history; a chart of it invites a trend reading
+    // that is not there.
+    renderSchoolDetail({
+      ...primaryFixture,
+      admissionDistance: cutoff({ distance_m: 700, year: 2024 }),
+      admissionDistanceHistory: history([[2024, 700]]),
+    });
+
+    expect(screen.queryByRole('button', { name: 'Distance' })).not.toBeInTheDocument();
+  });
+
+  it('lists every year in the span, including the ones with no figure', () => {
+    renderSchoolDetail({
+      ...primaryFixture,
+      admissionDistance: cutoff({ distance_m: 700, year: 2024 }),
+      admissionDistanceHistory: history([[2021, 1000], [2024, 700]]),
+    });
+
+    // The view is server-rendered but starts hidden behind its tab, and role
+    // queries skip hidden subtrees — so open it the way a reader would.
+    fireEvent.click(screen.getByRole('button', { name: 'Distance' }));
+
+    // 2022 and 2023 were never published but must still appear as rows, or the
+    // gap in the chart has nothing explaining it.
+    for (const year of ['2021', '2022', '2023', '2024']) {
+      expect(screen.getByRole('rowheader', { name: year })).toBeInTheDocument();
+    }
+    expect(screen.getAllByText('Not published').length).toBe(2);
+  });
+
+  it('never claims everyone was offered a place', () => {
+    // fact_admissions.oversubscribed is about first preferences only, so the
+    // stronger claim is not supported by the data behind it.
+    renderSchoolDetail({
+      ...primaryFixture,
+      admissionDistance: cutoff({ distance_m: 700, year: 2024 }),
+      admissionDistanceHistory: history([[2021, 1000], [2024, 700]]),
+      admissionsHistory: [
+        ...primaryFixture.admissionsHistory,
+        { year: 2022, oversubscribed: false, places_offered: 60 },
+      ],
+    });
+
+    expect(screen.getByText(/Places available on first preferences/)).toBeInTheDocument();
+    expect(screen.queryByText(/every applicant/i)).not.toBeInTheDocument();
+    expect(screen.queryByText(/all offered/i)).not.toBeInTheDocument();
+  });
+
+  it('withholds a trend reading while the record is thin', () => {
+    renderSchoolDetail({
+      ...primaryFixture,
+      admissionDistance: cutoff({ distance_m: 700, year: 2024 }),
+      admissionDistanceHistory: history([[2023, 800], [2024, 700]]),
+    });
+
+    expect(screen.getByText(/too few to read as a trend/)).toBeInTheDocument();
+    expect(screen.queryByText(/Across \d+ published years/)).not.toBeInTheDocument();
+  });
+});
+
+describe('secondary Distance detail', () => {
+  it('renders inline, with no extra tab, once there are two published years', () => {
+    renderSecondarySchoolDetail({
+      ...secondaryFixture,
+      admissionDistance: cutoff({ distance_m: 3472.96 }),
+      admissionDistanceHistory: history([[2023, 3800], [2024, 3472.96]]),
+    });
+
+    expect(screen.getByText(/Last distance offered, by year/)).toBeInTheDocument();
+    expect(screen.getByRole('rowheader', { name: '2023' })).toBeInTheDocument();
+  });
+
+  it('explains a selective school by how it admits rather than as missing data', () => {
+    renderSecondarySchoolDetail({
+      ...secondaryFixture,
+      schoolInfo: { ...secondaryFixture.schoolInfo, admissions_policy: 'Selective' },
+      admissionDistance: null,
+      admissionDistanceHistory: [],
+    });
+
+    expect(screen.getByText(/ranked by the entrance test/)).toBeInTheDocument();
+    expect(screen.queryByText(/has not published a cut-off distance/)).not.toBeInTheDocument();
+  });
+
+  it('reads a consistently undersubscribed school as good news', () => {
+    renderSecondarySchoolDetail({
+      ...secondaryFixture,
+      admissionDistance: null,
+      admissionDistanceHistory: [],
+      admissionsHistory: [
+        { year: 2022, oversubscribed: false },
+        { year: 2023, oversubscribed: false },
+        { year: 2024, oversubscribed: false },
+      ],
+    });
+
+    expect(screen.getByText(/has not needed a distance cut-off/)).toBeInTheDocument();
+  });
+});