feat(schools): label age range as "Ages 3–11" for clarity

The bare "3-11" range gave no unit. Add a display-only formatAgeRange
helper ("3-11" -> "Ages 3–11", en-dash) used in the primary/secondary
search rows and the secondary detail badge. The raw age_range field is
left untouched so sixth-form detection (.includes('18')) still works.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nextjs-app/lib/utils.ts

@@ -59,6 +59,18 @@ export function truncate(text: string, maxLength: number): string {
   return text.slice(0, maxLength).trim() + '...';
 }
 
+/**
+ * Format a school's age range for display, e.g. "3-11" → "Ages 3–11".
+ * Display-only — leaves the raw `age_range` field (used for sixth-form
+ * detection) untouched. Falls back to the raw value if it's not a plain range.
+ */
+export function formatAgeRange(ageRange: string | null | undefined): string {
+  if (!ageRange) return '';
+  const match = ageRange.match(/^\s*(\d+)\s*[-–]\s*(\d+)\s*$/);
+  if (!match) return ageRange;
+  return `Ages ${match[1]}–${match[2]}`;
+}
+
 // ============================================================================
 // Number Formatting
 // ============================================================================