Harden export preview handling

frontend/src/App.tsx

@@ -9,6 +9,7 @@ import { DatasetDetailPanel } from './components/datasets/DatasetDetailPanel'
 import { DatasetPanel } from './components/datasets/DatasetPanel'
 import { DetectionLab } from './components/detection/DetectionLab'
 import { ExportCenter } from './components/exports/ExportCenter'
+import { ExportPreview } from './components/exports/ExportPreview'
 import { MapWorkspace } from './components/map/MapWorkspace'
 import { AreaPanel } from './components/project/AreaPanel'
 import { ProjectPanel } from './components/project/ProjectPanel'
@@ -740,12 +741,7 @@ function App(): JSX.Element {
           onPreviewContent={previewExportContent}
           onDownload={downloadExportArtifact}
         />
-        {exportPreview ? (
-          <section>
-            <h2>Export Preview</h2>
-            <pre className="job-result">{JSON.stringify(exportPreview, null, 2)}</pre>
-          </section>
-        ) : null}
+        <ExportPreview content={exportPreview} />
 
         <DatasetPanel
           selectedProjectId={selectedProjectId}