fix: thread environment into correlation-chain query in ExchangeHeader

The env-scoping migration (P3A) changed useCorrelationChain to require an
environment arg and gate on `enabled: !!correlationId && !!environment`,
but ExchangeHeader was still calling it with one arg. Result: the query
never fired, so the header always rendered "no correlated exchanges
found" even when 4+ exchanges shared a correlationId.

Fix: read the selected env from the Zustand environment store and pass
it through.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/Exchanges/ExchangeHeader.tsx

@@ -6,6 +6,7 @@ import { useCorrelationChain } from '../../api/queries/correlation';
 import { useAgents } from '../../api/queries/agents';
 import { useCatalog } from '../../api/queries/catalog';
 import { useCanControl } from '../../auth/auth-store';
+import { useEnvironmentStore } from '../../api/environment-store';
 import type { ExecutionDetail } from '../../components/ExecutionDiagram/types';
 import { attributeBadgeColor } from '../../utils/attribute-color';
 import { formatDuration, statusLabel } from '../../utils/format-utils';
@@ -32,7 +33,8 @@ function statusVariant(s: string): StatusVariant {
 export function ExchangeHeader({ detail, onCorrelatedSelect, onClearSelection }: ExchangeHeaderProps) {
   const navigate = useNavigate();
   const { timeRange } = useGlobalFilters();
-  const { data: chainResult } = useCorrelationChain(detail.correlationId ?? null);
+  const environment = useEnvironmentStore((s) => s.environment);
+  const { data: chainResult } = useCorrelationChain(detail.correlationId ?? null, environment);
   const chain = chainResult?.data;
   const showChain = chain && chain.length > 1;
   const attrs = Object.entries(detail.attributes ?? {});