fix(free-layout-demo): fix loop subcanvas error (#340)

apps/demo-free-layout/src/nodes/loop/loop-form-render.tsx

@@ -1,4 +1,5 @@
 import { FormRenderProps, FlowNodeJSON, Field } from '@flowgram.ai/free-layout-editor';
+import { SubCanvasRender } from '@flowgram.ai/free-container-plugin';
 import { BatchVariableSelector, IFlowRefValue } from '@flowgram.ai/form-materials';
 
 import { useIsSidebar, useNodeRenderContext } from '../../hooks';
@@ -47,6 +48,7 @@ export const LoopFormRender = ({ form }: FormRenderProps<LoopNodeJSON>) => {
       <FormHeader />
       <FormContent>
         {batchFor}
+        <SubCanvasRender />
         <FormOutputs />
       </FormContent>
     </>