feat(search): filter on phones through one sheet

On phones the results toolbar's filters were a sideways-scrolling row
led by "More filters", so phase showed only in part and school type not
at all, and the panel "More filters" opened held neither of them.

Phones now get a single Filters button beside the folded search summary,
counting every applied filter. It opens a bottom sheet with every filter:
distance as five segments, then phase, school type, local authority and
the secondary-only filters. Changes apply at once, as on desktop, so the
footer's "Show N schools" only closes the sheet. Applied filters show as
removable chips on a second line, which appears only when something is
applied. Desktop and tablet are unchanged.

Modal gains dialog semantics, a pinned footer and focus handling, and
moves above the pinned toolbar, the floating List/Map button and the
comparison toast, which its old z-index sat beneath.

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

e2e/tests/journeys.spec.ts

@@ -712,12 +712,13 @@ for (const width of [360, 390, 402, 430]) {
     // scrollWidth alone cannot see this page's overflow: .main clips on x, so
     // the search summary ran 40px off an iPhone 17 screen with scrollWidth
     // still equal to the viewport. Measure the toolbar's own edges instead;
-    // the controls row scrolls by design, so only its box is held to the edge.
+    // the applied-filter chips scroll by design, so only their line's box is
+    // held to the edge.
     const offscreen = await page.evaluate(() => {
       const toolbar = document.querySelector('[class*="resultsToolbar"]');
       return [...(toolbar?.querySelectorAll('*') ?? [])]
         .filter((el) => (el as HTMLElement).offsetParent
-          && !el.parentElement?.closest('[class*="controlsRow"]'))
+          && !el.parentElement?.closest('[class*="chipsLine"]'))
         .map((el) => ({ el: (el.className?.toString() || el.tagName).slice(0, 40),
           right: Math.round(el.getBoundingClientRect().right) }))
         .filter((o) => o.right > window.innerWidth);
@@ -749,6 +750,67 @@ for (const width of [360, 390, 402, 430]) {
   });
 }
 
+/*
+ * Phones filter through one Filters button and a sheet with every filter in
+ * it. The row it replaced scrolled sideways with "More filters" first, so
+ * phase showed only in part, school type not at all, and the panel "More
+ * filters" opened held neither.
+ */
+test('a phone filters through one sheet, and sees what it applied as chips', async ({ page }) => {
+  await page.setViewportSize({ width: 390, height: 844 });
+  await page.goto(LONG_LIST);
+  const trigger = page.getByRole('button', { name: 'Filters', exact: true });
+  await expect(trigger).toBeInViewport({ timeout: 15_000 });
+  // The desktop row is gone at this width: no phase select until the sheet.
+  await expect(page.getByRole('combobox', { name: 'Phase', exact: true })).toHaveCount(0);
+
+  await trigger.click();
+  const sheet = page.getByRole('dialog', { name: 'Filters' });
+  await expect(sheet).toBeVisible();
+  await expect(sheet.getByRole('radio', { name: 'Within 1 mile' })).toBeChecked();
+  for (const name of ['Phase', 'School type', 'Local authority']) {
+    await expect(sheet.getByRole('combobox', { name, exact: true })).toBeVisible();
+  }
+
+  // A change applies at once, and the sheet stays open for the next one.
+  await sheet.getByRole('combobox', { name: 'Phase', exact: true }).selectOption('primary');
+  await page.waitForURL(/[?&]phase=primary(&|$)/);
+  await expect(sheet).toBeVisible();
+  const show = sheet.getByRole('button', { name: /^(Show [\d,]+ schools?|No schools match)$/ });
+  await expect(show).toBeVisible();
+
+  // MOBILE.md: the sheet clears the bottom tab bar, and its targets are 44px.
+  // It slides up over 0.3s, so poll for where it comes to rest.
+  await expect.poll(async () => {
+    const box = (await show.boundingBox())!;
+    return Math.round(box.y + box.height);
+  }).toBeLessThanOrEqual(844);
+  const small = await sheet.evaluate((el) =>
+    [...el.querySelectorAll('button, select, label:has(input)')]
+      .filter((n): n is HTMLElement => !!(n as HTMLElement).offsetParent)
+      .map((n) => ({ t: n.innerText?.trim().slice(0, 24) || n.getAttribute('aria-label'),
+        w: n.getBoundingClientRect().width, h: n.getBoundingClientRect().height }))
+      .filter((o) => o.w < 44 || o.h < 44));
+  expect(small).toEqual([]);
+
+  await show.click();
+  await expect(sheet).toBeHidden();
+
+  // What was applied shows under the search, counted on the button, and comes
+  // off with a tap, keeping the search.
+  await expect(page.getByRole('button', { name: 'Filters, 1 applied' })).toBeInViewport();
+  const chip = page.getByRole('group', { name: 'Applied filters' })
+    .getByRole('button', { name: 'Remove filter: Primary' });
+  await expect(chip).toBeInViewport();
+  expect(await page.evaluate(() => document.documentElement.scrollWidth - window.innerWidth))
+    .toBe(0);
+  await chip.click();
+  await expect(page).not.toHaveURL(/[?&]phase=/);
+  await expect(page).toHaveURL(/[?&]postcode=B1(%20|\+)1BB/);
+  await expect(page.getByRole('group', { name: 'Applied filters' })).toHaveCount(0);
+  await expect(trigger).toBeInViewport();
+});
+
 test('comparing two schools shows the parent-first sections side by side', async ({ page }) => {
   // Two same-phase (pure primary) schools so both stay on one tab.
   const [urn0, urn1] = await twoPrimaryUrns(page);