fix(ui/alerts): bulk-read body uses instanceIds to match BulkReadRequest DTO

Plan 03 prose had 'alertInstanceIds'; backend record is 'instanceIds'.

ui/src/api/queries/alerts.ts

@@ -155,7 +155,7 @@ export function useBulkReadAlerts() {
         '/environments/{envSlug}/alerts/bulk-read',
         {
           params: { path: { envSlug: env } },
-          body: { alertInstanceIds: ids },
+          body: { instanceIds: ids },
         } as any,
       );
       if (error) throw error;