Fix metrics API response structure

Backend returns metrics as an array, not an object.
- Update MetricsResponse type to use MetricDefinition[] instead of Record
- Remove Object.values() conversion in compare and rankings pages
- Fix useMetrics hook to handle array instead of object
- Fix getMetric to use array.find() instead of object indexing

Fixes empty metric dropdown on compare page.

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

nextjs-app/app/compare/page.tsx

@@ -44,8 +44,8 @@ export default async function ComparePage({ searchParams }: ComparePageProps) {
     // Fetch available metrics
     const metricsResponse = await fetchMetrics();
 
-    // Convert metrics object to array
-    const metricsArray = Object.values(metricsResponse?.metrics || {});
+    // Metrics is already an array
+    const metricsArray = metricsResponse?.metrics || [];
 
     return (
       <ComparisonView

nextjs-app/app/rankings/page.tsx

@@ -43,8 +43,8 @@ export default async function RankingsPage({ searchParams }: RankingsPageProps)
       fetchMetrics(),
     ]);
 
-    // Convert metrics object to array
-    const metricsArray = Object.values(metricsResponse?.metrics || {});
+    // Metrics is already an array
+    const metricsArray = metricsResponse?.metrics || [];
 
     return (
       <RankingsView

nextjs-app/hooks/useMetrics.ts

@@ -19,9 +19,9 @@ export function useMetrics() {
   );
 
   return {
-    metrics: data?.metrics || {},
-    metricsList: data?.metrics ? Object.values(data.metrics) : [],
-    getMetric: (key: string) => data?.metrics?.[key],
+    metrics: data?.metrics || [],
+    metricsList: data?.metrics || [],
+    getMetric: (key: string) => data?.metrics?.find(m => m.key === key),
     isLoading,
     error,
   };

nextjs-app/lib/types.ts

@@ -194,8 +194,9 @@ export interface MetricDefinition {
   hasNationalAverage?: boolean;
 }
 
+// Backend returns metrics as an array, not an object
 export interface MetricsResponse {
-  metrics: Record<string, MetricDefinition>;
+  metrics: MetricDefinition[];
 }
 
 export interface DataInfoResponse {