feat(ui): show agent ID in exchange header info row

ui/src/pages/Exchanges/ExchangeHeader.tsx

@@ -61,6 +61,12 @@ export function ExchangeHeader({ detail }: ExchangeHeaderProps) {
         <span className={styles.route}>{detail.routeId}</span>
         <span className={styles.app}>{detail.applicationName}</span>
         <span className={styles.duration}>{formatDuration(detail.durationMs)}</span>
+        {detail.agentId && (
+          <>
+            <span className={styles.separator} />
+            <MonoText size="xs">{detail.agentId}</MonoText>
+          </>
+        )}
       </div>
 
       {/* Correlation chain — only when multiple correlated exchanges exist */}