feat(rankings,metrics): score visible on phones; definitions usable everywhere (P2.2, P2.3)

Rankings mobile: the metric value — the point of the page — sat behind
a sideways swipe at 390px. The Area column now folds into a subline
under the school name, leaving Rank | School | Value to fit the
viewport with no horizontal scroll.

Rankings default metric becomes 'expected standard' (rwm_expected_pct);
'higher standard' stays available but no longer frames every school's
headline number in the terms parents least understand.

MetricTooltip was hover-only and display:none on phones — the mobile-
primary audience had zero access to the Attainment 8 / Progress 8 /
EBacc definitions. It is now a real button: tap/click/keyboard
toggleable with outside-click and Escape dismissal, 24px target,
shown at all viewports.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nextjs-app/app/rankings/page.tsx

@@ -29,7 +29,7 @@ export default async function RankingsPage({ searchParams }: RankingsPageProps)
   const { metric: metricParam, local_authority, year: yearParam, phase: phaseParam } = await searchParams;
 
   const phase = phaseParam || 'primary';
-  const metric = metricParam || (phase === 'secondary' ? 'attainment_8_score' : 'rwm_high_pct');
+  const metric = metricParam || (phase === 'secondary' ? 'attainment_8_score' : 'rwm_expected_pct');
   const year = yearParam ? parseInt(yearParam) : undefined;
 
   // Fetch rankings data with error handling