fix(export): send credentials and surface server error on USFM export

src/features/projects/components/ExportProjectDialog.tsx

@@ -115,7 +115,7 @@ export const ExportProjectDialog: React.FC<ExportProjectDialogProps> = ({
 
       onClose();
     } catch (err) {
-      setError('Export Failed');
+      setError(err instanceof Error ? err.message : 'Export Failed');
       Logger.logException(err, {
         context: 'Export failed',
         projectUnitId,

src/features/projects/hooks/useExportUsfm.ts

@@ -7,16 +7,32 @@ interface ExportUsfmPayload {
   bookIds: number[];
 }
 
+const DEFAULT_EXPORT_ERROR = 'Failed to export USFM';
+
+// The export endpoint streams a ZIP on success and returns a JSON error body
+// otherwise. Surface the server's message (supports both the `{ message }`
+// envelope and the USFM route's `{ error }` shape) so the dialog can show
+// something actionable instead of a generic failure.
+const parseExportError = async (response: Response): Promise<string> => {
+  try {
+    const data = (await response.json()) as { message?: string; error?: string };
+    return data.message ?? data.error ?? DEFAULT_EXPORT_ERROR;
+  } catch {
+    return DEFAULT_EXPORT_ERROR;
+  }
+};
+
 const exportUsfmRequest = async (payload: ExportUsfmPayload): Promise<Blob> => {
   const { projectUnitId, bookIds } = payload;
 
   const response = await fetch(`${config.api.url}/project-units/${projectUnitId}/usfm`, {
     method: 'POST',
+    credentials: 'include',
     headers: { 'Content-Type': 'application/json' },
     body: JSON.stringify({ bookIds }),
   });
 
-  if (!response.ok) throw new Error('Failed to export USFM');
+  if (!response.ok) throw new Error(await parseExportError(response));
 
   return response.blob();
 };