feat(ui): add phase indicators to school list rows

Add coloured left-border and phase label pill to visually differentiate
school phases (Primary, Secondary, All-through, Post-16, Nursery) in
search result lists. Colours are accessible (WCAG AA) and don't clash
with existing Ofsted/trend semantic colours.

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

nextjs-app/lib/utils.ts

@@ -364,6 +364,25 @@ export function parseQueryString(search: string): Record<string, string> {
  * Handles both 4-digit start years (2023 → "2023/24") and
  * 6-digit EES codes (202526 → "2025/26").
  */
+export function getPhaseStyle(phase?: string | null): { key: string; label: string } {
+  switch (phase?.toLowerCase()) {
+    case 'primary':
+    case 'middle deemed primary':
+      return { key: 'Primary', label: 'Primary' };
+    case 'secondary':
+    case 'middle deemed secondary':
+      return { key: 'Secondary', label: 'Secondary' };
+    case 'all-through':
+      return { key: 'AllThrough', label: 'All-through' };
+    case '16 plus':
+      return { key: 'Post16', label: 'Post-16' };
+    case 'nursery':
+      return { key: 'Nursery', label: 'Nursery' };
+    default:
+      return { key: '', label: '' };
+  }
+}
+
 export function formatAcademicYear(year: number): string {
   const s = year.toString();
   if (s.length === 6) {