fix(compare): align sticky school chips with their data columns on desktop

The bar was a plain flex row while sections use a 200px-label + per-school
grid, so chips drifted off the columns they label. The bar now shares the
sections' grid template (via --school-count) at the same 761px breakpoint;
verified pixel-exact against live section columns (236/615/994). Mobile
pills unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

e2e/tests/journeys.spec.ts

@@ -197,6 +197,14 @@ test('comparing two schools shows the parent-first sections side by side', async
   // Every number gets an anchor: at least one England-average tick or label
   await expect(page.getByText(/England \d+/).first()).toBeVisible();
 
+  // Desktop: the sticky school bar shares the sections' grid template
+  // (200px label rail + one column per school) so chips align with the
+  // columns they label.
+  const barTemplate = await page
+    .locator('[aria-label="Schools in this comparison"]')
+    .evaluate((el) => getComputedStyle(el).gridTemplateColumns);
+  expect(barTemplate).toMatch(/^200px /);
+
   // Ofsted linkout goes to the school's provider page, never a report deep-link
   const ofstedLink = page.getByRole('link', { name: /Ofsted page/i }).first();
   await expect(ofstedLink).toBeVisible();