fix(ui): exchange selection uses state, not URL navigation

Row click no longer navigates to /exchanges/:app/:route/:id which was
changing the search scope. Instead, Dashboard calls onExchangeSelect
callback and ExchangesPage manages the selected exchange as local state.
The search criteria and scope are preserved when selecting an exchange.

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

ui/src/pages/Dashboard/Dashboard.tsx

@@ -176,7 +176,17 @@ function buildBaseColumns(): Column<Row>[] {
 
 // ─── Dashboard component ─────────────────────────────────────────────────────
 
-export default function Dashboard() {
+export interface SelectedExchange {
+  executionId: string;
+  applicationName: string;
+  routeId: string;
+}
+
+interface DashboardProps {
+  onExchangeSelect?: (exchange: SelectedExchange) => void;
+}
+
+export default function Dashboard({ onExchangeSelect }: DashboardProps = {}) {
   const { appId, routeId } = useParams<{ appId: string; routeId: string }>()
   const navigate = useNavigate()
   const [searchParams, setSearchParams] = useSearchParams()
@@ -228,8 +238,13 @@ export default function Dashboard() {
 
   function handleRowClick(row: Row) {
     setSelectedId(row.id)
-    // Navigate to the split view with diagram
-    navigate(`/exchanges/${row.applicationName}/${row.routeId}/${row.executionId}`)
+    if (onExchangeSelect) {
+      onExchangeSelect({
+        executionId: row.executionId,
+        applicationName: row.applicationName ?? '',
+        routeId: row.routeId,
+      })
+    }
   }
 
   function handleRowAccent(row: Row): 'error' | 'warning' | undefined {