Add promptUserNumber to showcase (#849)

It was missing.

src/frontend/src/showcase.ts

@@ -41,6 +41,7 @@ import { verifyDevice } from "./flows/addDevice/manage/verifyTentativeDevice";
 import { withLoader } from "./components/loader";
 import { displaySafariWarning } from "./flows/recovery/displaySafariWarning";
 import { displayError } from "./components/displayError";
+import { promptUserNumber } from "./flows/promptUserNumber";
 
 // A "dummy" connection which actually is just undefined, hoping pages won't call it
 const dummyConnection = undefined as unknown as AuthenticatedConnection;
@@ -154,6 +155,7 @@ const iiPages: Record<string, () => void> = {
       detail: "oh my, so much to say. SO MUCH!",
       primaryButton: "Try again",
     }),
+  promptUserNumber: () => promptUserNumber("hello", null),
 };
 
 // The showcase