Fix filters API response structure

Backend returns filters directly at top level, not wrapped in 'filters' property.
Update FiltersResponse type and page components to match actual API response.

Fixes empty dropdowns for school types and local authorities.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

nextjs-app/app/page.tsx

@@ -48,7 +48,7 @@ export default async function HomePage({ searchParams }: HomePageProps) {
     return (
       <HomeView
         initialSchools={schoolsData}
-        filters={filtersData?.filters || { local_authorities: [], school_types: [], years: [] }}
+        filters={filtersData || { local_authorities: [], school_types: [], years: [] }}
       />
     );
   } catch (error) {

nextjs-app/app/rankings/page.tsx

@@ -49,7 +49,7 @@ export default async function RankingsPage({ searchParams }: RankingsPageProps)
     return (
       <RankingsView
         rankings={rankingsResponse?.rankings || []}
-        filters={filtersResponse?.filters || { local_authorities: [], school_types: [], years: [] }}
+        filters={filtersResponse || { local_authorities: [], school_types: [], years: [] }}
         metrics={metricsArray}
         selectedMetric={metric}
         selectedArea={local_authority}