fix(search): address review on the shared result rows

- The rows' narrow layout now switches at a 608px list, not 600px. Below
  769px the page pads 1rem each side, so a 640px screen gives a 608px
  list: exactly the old max-width: 640px media query, where 600px left
  633-640px screens on the wide layout.
- rowContainerGuard.test.ts fails if anything other than HomeView renders
  SchoolRow or SecondarySchoolRow, or if one of HomeView's row lists loses
  its `results` container. Outside one the rows silently keep their wide
  layout on phones. (Checked: HomeView is the only importer today.)
- Picking a pin from the list beside the map now works from the keyboard:
  each row carries a "Show <school> on the map" button, visually hidden
  until focused, with aria-pressed for the selected school. The row itself
  cannot be the button, since it holds links and buttons of its own.

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

e2e/tests/journeys.spec.ts

@@ -578,6 +578,17 @@ test('a desktop postcode search opens on the map with the list beside it', async
   await card.click({ position: { x: 6, y: 6 } });
   await expect(page.locator('.sc-pin--selected')).toHaveCount(1);
   await expect(page.locator('.sc-popup')).toContainText(name);
+
+  // And from the keyboard: each row has a "Show … on the map" button that
+  // appears on focus.
+  const second = pane.locator('[data-urn]').nth(1);
+  const secondName = (await second.locator('a').first().innerText()).trim();
+  const show = second.getByRole('button', { name: `Show ${secondName} on the map` });
+  await show.focus();
+  await expect(show).toBeVisible();
+  await page.keyboard.press('Enter');
+  await expect(show).toHaveAttribute('aria-pressed', 'true');
+  await expect(page.locator('.sc-popup')).toContainText(secondName);
 });
 
 // 402 is the iPhone 17, where the toolbar overflowed (see below).