fix(school): show Nursery only for nursery classes, and say Girls' school

GIAS NurseryProvision is text ("Has Nursery Classes", "No Nursery
Classes", "Not applicable"), but the header and the place table tested it
for truthiness. Every school with a value got a Nursery chip or a "Yes",
including secondaries aged 11-18. hasNurseryClasses() matches the one
value that means a nursery, and the type now says the field is a string.

The single-sex chip appended 's to the plural GIAS gender, giving
"Girls's school". singleSexLabel() gives "Girls' school" / "Boys' school".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

nextjs-app/lib/utils.ts

@@ -99,6 +99,25 @@ export function formatAgeRange(ageRange: string | null | undefined): string {
   return /^\d+–\d+$/.test(span) ? `Ages ${span}` : span;
 }
 
+/**
+ * GIAS NurseryProvision is text: "Has Nursery Classes", "No Nursery Classes"
+ * or "Not applicable". Only the first means a nursery, so never test the raw
+ * value for truthiness.
+ */
+export function hasNurseryClasses(value: string | null | undefined): boolean {
+  return value?.trim().toLowerCase() === 'has nursery classes';
+}
+
+/**
+ * "Girls' school" / "Boys' school" for a single-sex school, null otherwise.
+ * GIAS genders are plural, so the possessive is a bare apostrophe.
+ */
+export function singleSexLabel(gender: string | null | undefined): string | null {
+  const g = gender?.trim();
+  if (g === 'Girls' || g === 'Boys') return `${g}' school`;
+  return null;
+}
+
 // ============================================================================
 // Number Formatting
 // ============================================================================