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/components/places/PlaceView.tsx

@@ -13,7 +13,7 @@ import Link from 'next/link';
 import type { PlaceDetail, PlaceSummary } from '@/lib/places';
 import { placeUrl, authoritySlug } from '@/lib/places';
 import type { School } from '@/lib/types';
-import { schoolUrl, formatAgeSpan } from '@/lib/utils';
+import { schoolUrl, formatAgeSpan, hasNurseryClasses } from '@/lib/utils';
 import { absoluteUrl } from '@/lib/site';
 import { TrackPlaceView } from './TrackPlaceView';
 import styles from './PlaceView.module.css';
@@ -131,9 +131,10 @@ function SchoolTable({ schools, phase }: { schools: School[]; phase: PhaseKey })
                 {showNursery && (
                   <td className={styles.attr}>
                     {/* Undefined is a mart the pipeline has not rebuilt, and
-                        false is a school without one. Neither is a "Yes", and
-                        neither is worth two different words. */}
-                    {s.nursery_provision ? 'Yes' : NO_VALUE}
+                        "No Nursery Classes" or "Not applicable" is a school
+                        without one. None is a "Yes", and none is worth a
+                        different word. */}
+                    {hasNurseryClasses(s.nursery_provision) ? 'Yes' : NO_VALUE}
                   </td>
                 )}
                 <td className={styles.attrWide}>