feat: add secondary school support with KS4 data and metric tooltips

- Backend: replace INNER JOIN ks2 with UNION ALL (ks2 + ks4) so primary
  and secondary schools both appear in the main DataFrame
- Backend: add /api/national-averages endpoint computing means from live
  data, replacing the hardcoded NATIONAL_AVG constant on the frontend
- Backend: add phase filter param to /api/schools; return phases from
  /api/filters; fix hardcoded "phase": "Primary" in school detail endpoint
- Backend: add KS4 metric definitions (Attainment 8, Progress 8, EBacc,
  English & Maths pass rates) to METRIC_DEFINITIONS and RANKING_COLUMNS
- Frontend: SchoolDetailView is now phase-aware — secondary schools show
  a GCSE Results section (Att8, P8, E&M, EBacc) instead of SATs; phonics
  tab hidden for secondary; admissions says Year 7 instead of Year 3;
  history table shows KS4 columns; chart datasets switch for secondary
- Frontend: new MetricTooltip component (CSS-only ⓘ icon) backed by
  METRIC_EXPLANATIONS — added to RWM, GPS, SEN, EAL, IDACI, progress
  scores and all KS4 metrics throughout SchoolDetailView and SchoolCard
- Frontend: METRIC_EXPLANATIONS extended with KS4 terms (Attainment 8,
  Progress 8, EBacc) and previously missing terms (SEN, EHCP, EAL, IDACI)
- Frontend: SchoolCard expands "RWM" to "Reading, Writing & Maths" and
  shows Attainment 8 / English & Maths Grade 4+ for secondary schools
- Frontend: FilterBar adds Phase dropdown (Primary / Secondary / All-through)
- Frontend: HomeView hero copy updated; compact list shows phase-aware metric
- Global metadata updated to remove "primary only" framing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nextjs-app/components/PerformanceChart.tsx

@@ -34,24 +34,50 @@ ChartJS.register(
 interface PerformanceChartProps {
   data: SchoolResult[];
   schoolName: string;
+  isSecondary?: boolean;
 }
 
-export function PerformanceChart({ data, schoolName }: PerformanceChartProps) {
+export function PerformanceChart({ data, schoolName, isSecondary = false }: PerformanceChartProps) {
   // Sort data by year
   const sortedData = [...data].sort((a, b) => a.year - b.year);
   const years = sortedData.map(d => d.year.toString());
 
-  // Prepare datasets
-  const datasets = [
+  // Prepare datasets — phase-aware
+  const datasets = isSecondary ? [
     {
-      label: 'RWM Expected %',
+      label: 'Attainment 8',
+      data: sortedData.map(d => d.attainment_8_score),
+      borderColor: 'rgb(59, 130, 246)',
+      backgroundColor: 'rgba(59, 130, 246, 0.1)',
+      tension: 0.3,
+      yAxisID: 'y',
+    },
+    {
+      label: 'English & Maths Grade 4+',
+      data: sortedData.map(d => d.english_maths_standard_pass_pct),
+      borderColor: 'rgb(16, 185, 129)',
+      backgroundColor: 'rgba(16, 185, 129, 0.1)',
+      tension: 0.3,
+      yAxisID: 'y',
+    },
+    {
+      label: 'Progress 8',
+      data: sortedData.map(d => d.progress_8_score),
+      borderColor: 'rgb(245, 158, 11)',
+      backgroundColor: 'rgba(245, 158, 11, 0.1)',
+      tension: 0.3,
+      yAxisID: 'y1',
+    },
+  ] : [
+    {
+      label: 'Reading, Writing & Maths Expected %',
       data: sortedData.map(d => d.rwm_expected_pct),
       borderColor: 'rgb(59, 130, 246)',
       backgroundColor: 'rgba(59, 130, 246, 0.1)',
       tension: 0.3,
     },
     {
-      label: 'RWM Higher %',
+      label: 'Reading, Writing & Maths Higher %',
       data: sortedData.map(d => d.rwm_high_pct),
       borderColor: 'rgb(16, 185, 129)',
       backgroundColor: 'rgba(16, 185, 129, 0.1)',
@@ -153,14 +179,14 @@ export function PerformanceChart({ data, schoolName }: PerformanceChartProps) {
         position: 'left' as const,
         title: {
           display: true,
-          text: 'Percentage (%)',
+          text: isSecondary ? 'Score / Percentage (%)' : 'Percentage (%)',
           font: {
             size: 12,
             weight: 'bold',
           },
         },
         min: 0,
-        max: 100,
+        max: isSecondary ? undefined : 100,
         grid: {
           color: 'rgba(0, 0, 0, 0.05)',
         },
@@ -171,7 +197,7 @@ export function PerformanceChart({ data, schoolName }: PerformanceChartProps) {
         position: 'right' as const,
         title: {
           display: true,
-          text: 'Progress Score',
+          text: isSecondary ? 'Progress 8 Score' : 'Progress Score',
           font: {
             size: 12,
             weight: 'bold',