feat(map): fetch all schools for map view, add reference pin, cap radius at 5mi

- Remove 10-mile radius option; cap backend radius max at 5 miles
- Raise backend page_size max to 500 so map can fetch all schools in one call
- HomeView: when map view is active, fetch all schools within radius
  (page_size=500) instead of showing only the paginated first page;
  falls back to initial SSR schools while loading
- SchoolMap/LeafletMapInner: accept referencePoint prop and render a
  distinctive coral circle pin at the search postcode location

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

nextjs-app/components/SchoolMap.tsx

@@ -24,10 +24,11 @@ interface SchoolMapProps {
   schools: School[];
   center?: [number, number];
   zoom?: number;
+  referencePoint?: [number, number];
   onMarkerClick?: (school: School) => void;
 }
 
-export function SchoolMap({ schools, center, zoom = 13, onMarkerClick }: SchoolMapProps) {
+export function SchoolMap({ schools, center, zoom = 13, referencePoint, onMarkerClick }: SchoolMapProps) {
   // Calculate center if not provided
   const mapCenter: [number, number] = center || (() => {
     if (schools.length === 0) return [51.5074, -0.1278]; // Default to London
@@ -50,6 +51,7 @@ export function SchoolMap({ schools, center, zoom = 13, onMarkerClick }: SchoolM
         schools={schools}
         center={mapCenter}
         zoom={zoom}
+        referencePoint={referencePoint}
         onMarkerClick={onMarkerClick}
       />
     </div>