Add demo CAD kernel Controller, and typing to suit

We might be adding JSCAD soon and adding some guidance on the happy
path with good typing for the CadKernels is a good idea

related to #411

app/web/src/helpers/cadPackages/demoController.ts

@@ -0,0 +1,32 @@
+// not an actual and there fore not imported into index.ts in this folder,
+// this is boiler plate code for adding new integrations.
+
+import {
+  RenderArgs,
+  DefaultKernelExport,
+} from './common'
+
+export const render: DefaultKernelExport['render'] = async ({
+  code,
+  settings,
+}: RenderArgs) => {
+  // do your magic
+  return {
+    status: 'healthy',
+    message: {
+      type: 'message',
+      message: 'demo',
+      time: new Date()
+    },
+    objectData: {
+      data: 'any',
+      type: 'geometry'
+    }
+  }
+}
+
+const demoController: DefaultKernelExport = {
+  render,
+}
+
+export default demoController