feat: add is_replay flag to execution pipeline and UI

Detect replayed exchanges via X-Cameleer-Replay header during ingestion,
persist the flag through PostgreSQL and OpenSearch, and surface it in
the dashboard (amber replay icon) and exchange detail chain view.

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

ui/src/api/schema.d.ts

@@ -1504,6 +1504,7 @@ export interface components {
                 [key: string]: string;
             };
             hasTraceData: boolean;
+            isReplay: boolean;
         };
         SearchResultExecutionSummary: {
             data: components["schemas"]["ExecutionSummary"][];