feat(phase7.4): order rejection + resubmit flow

- Migration 053: rejection_reason TEXT NULL on orders table
- POST /api/orders/{id}/reject (PM+): sets rejected status, cancels
  active renders, stores reason, notifies creator, broadcasts WS event
- POST /api/orders/{id}/resubmit (creator or PM+): resets to draft,
  clears rejection fields, notifies PMs
- OrderDetail: Reject button (PM+) + inline modal with reason textarea
  and notify-client checkbox; Resubmit button; rejection reason amber
  alert box shown below header when order is rejected
- Orders Kanban: rejection_reason shown as red italic note on card
- Order interface: rejected_at, rejection_reason fields

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Orders.tsx

@@ -711,7 +711,12 @@ function KanbanCard({
       {rp && rp.total > 0 && (
         <RenderProgressBar progress={rp} />
       )}
-      {order.notes && !rp && (
+      {order.status === 'rejected' && order.rejection_reason && (
+        <p className="mt-2 text-xs text-red-500 italic truncate" title={order.rejection_reason}>
+          {order.rejection_reason}
+        </p>
+      )}
+      {order.notes && !rp && order.status !== 'rejected' && (
         <p className="mt-2 text-xs text-content-muted truncate">{order.notes}</p>
       )}
       <div className="mt-2 flex items-center justify-end opacity-0 group-hover:opacity-100 transition-opacity">