Fix missing avg duration comparison on route Performance tab

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/routes/PerformanceTab.tsx

@@ -45,6 +45,7 @@ export function PerformanceTab({ group, routeId }: PerformanceTabProps) {
   const prevFailureRate = stats && stats.prevTotalCount > 0
     ? (stats.prevFailedCount / stats.prevTotalCount) * 100 : 0;
 
+  const avgChange = stats ? pctChange(stats.avgDurationMs, stats.prevAvgDurationMs) : null;
   const p99Change = stats ? pctChange(stats.p99LatencyMs, stats.prevP99LatencyMs) : null;
   const failChange = stats ? pctChange(failureRate, prevFailureRate) : null;
 
@@ -63,6 +64,8 @@ export function PerformanceTab({ group, routeId }: PerformanceTabProps) {
           label="Avg Duration"
           value={stats ? `${stats.avgDurationMs}ms` : '--'}
           accent="cyan"
+          change={avgChange?.text}
+          changeDirection={avgChange?.direction}
           sparkData={sparkAvg}
         />
         <StatCard