feat(map): add fullscreen button using browser Fullscreen API

Button sits top-right of the map (matching Leaflet control style),
toggles expand/compress icon, and syncs state with Escape key via
the fullscreenchange event.

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

nextjs-app/components/SchoolMap.module.css

@@ -4,6 +4,34 @@
   position: relative;
 }
 
+.mapWrapper.fullscreen {
+  width: 100vw;
+  height: 100vh;
+}
+
+.fullscreenBtn {
+  position: absolute;
+  top: 0.625rem;
+  right: 0.625rem;
+  z-index: 1000;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 34px;
+  height: 34px;
+  background: white;
+  border: 2px solid rgba(0, 0, 0, 0.2);
+  border-radius: 4px;
+  cursor: pointer;
+  color: #333;
+  transition: background 0.15s ease, color 0.15s ease;
+}
+
+.fullscreenBtn:hover {
+  background: #f4f4f4;
+  color: #000;
+}
+
 .mapLoading {
   width: 100%;
   height: 100%;

nextjs-app/components/SchoolMap.tsx

@@ -6,6 +6,7 @@
 'use client';
 
 import dynamic from 'next/dynamic';
+import { useRef, useState, useEffect, useCallback } from 'react';
 import type { School } from '@/lib/types';
 import styles from './SchoolMap.module.css';
 
@@ -29,24 +30,59 @@ interface SchoolMapProps {
 }
 
 export function SchoolMap({ schools, center, zoom = 13, referencePoint, onMarkerClick }: SchoolMapProps) {
+  const wrapperRef = useRef<HTMLDivElement>(null);
+  const [isFullscreen, setIsFullscreen] = useState(false);
+
+  // Sync state with browser fullscreen events (e.g. Escape key)
+  useEffect(() => {
+    const onFsChange = () => setIsFullscreen(!!document.fullscreenElement);
+    document.addEventListener('fullscreenchange', onFsChange);
+    return () => document.removeEventListener('fullscreenchange', onFsChange);
+  }, []);
+
+  const toggleFullscreen = useCallback(() => {
+    if (!document.fullscreenElement) {
+      wrapperRef.current?.requestFullscreen();
+    } else {
+      document.exitFullscreen();
+    }
+  }, []);
+
   // Calculate center if not provided
   const mapCenter: [number, number] = center || (() => {
-    if (schools.length === 0) return [51.5074, -0.1278]; // Default to London
+    if (schools.length === 0) return [51.5074, -0.1278];
     if (schools.length === 1 && schools[0].latitude && schools[0].longitude) {
       return [schools[0].latitude, schools[0].longitude];
     }
-
-    // Calculate average position
     const validSchools = schools.filter(s => s.latitude && s.longitude);
     if (validSchools.length === 0) return [51.5074, -0.1278];
-
     const avgLat = validSchools.reduce((sum, s) => sum + (s.latitude || 0), 0) / validSchools.length;
     const avgLng = validSchools.reduce((sum, s) => sum + (s.longitude || 0), 0) / validSchools.length;
     return [avgLat, avgLng];
   })();
 
   return (
-    <div className={styles.mapWrapper}>
+    <div ref={wrapperRef} className={`${styles.mapWrapper} ${isFullscreen ? styles.fullscreen : ''}`}>
+      <button
+        className={styles.fullscreenBtn}
+        onClick={toggleFullscreen}
+        title={isFullscreen ? 'Exit fullscreen' : 'Fullscreen'}
+        aria-label={isFullscreen ? 'Exit fullscreen' : 'View map fullscreen'}
+      >
+        {isFullscreen ? (
+          /* Compress icon */
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" width="18" height="18" strokeLinecap="round" strokeLinejoin="round">
+            <path d="M8 3v3a2 2 0 0 1-2 2H3"/><path d="M21 8h-3a2 2 0 0 1-2-2V3"/>
+            <path d="M3 16h3a2 2 0 0 1 2 2v3"/><path d="M16 21v-3a2 2 0 0 1 2-2h3"/>
+          </svg>
+        ) : (
+          /* Expand icon */
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" width="18" height="18" strokeLinecap="round" strokeLinejoin="round">
+            <path d="M8 3H5a2 2 0 0 0-2 2v3"/><path d="M21 8V5a2 2 0 0 0-2-2h-3"/>
+            <path d="M3 16v3a2 2 0 0 0 2 2h3"/><path d="M16 21h3a2 2 0 0 0 2-2v-3"/>
+          </svg>
+        )}
+      </button>
       <LeafletMap
         schools={schools}
         center={mapCenter}