Fix undefined params reference in send button

Use designId prop instead of undefined params variable.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/components/DesignCanvas.tsx

@@ -1614,7 +1614,7 @@ export default function DesignCanvas({
               </button>
             ) : isAdminEditing ? (
               <button
-                onClick={() => handleSendToCustomerForReview(params?.id || '')}
+                onClick={() => handleSendToCustomerForReview(designId || '')}
                 disabled={submittingForApproval}
                 className={`flex-1 px-6 py-3 text-sm font-medium transition-colors ${
                   submittingForApproval