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/pages/Dashboard/Dashboard.tsx

@@ -1,6 +1,6 @@
 import { useState, useMemo, useCallback } from 'react'
 import { useParams, useNavigate, useSearchParams } from 'react-router'
-import { AlertTriangle, X, Search, Footprints } from 'lucide-react'
+import { AlertTriangle, X, Search, Footprints, RotateCcw } from 'lucide-react'
 import {
   DataTable,
   StatusDot,
@@ -79,6 +79,7 @@ function buildBaseColumns(): Column<Row>[] {
           <StatusDot variant={statusToVariant(row.status)} />
           <MonoText size="xs">{statusLabel(row.status)}</MonoText>
           {row.hasTraceData && <Footprints size={11} color="#3D7C47" style={{ marginLeft: 2, flexShrink: 0 }} />}
+          {row.isReplay && <RotateCcw size={11} color="var(--amber)" style={{ marginLeft: 2, flexShrink: 0 }} />}
         </span>
       ),
     },