Make the demo user interface accessible through the API

Add a new UI route to serve the interactive demo interface at `/api/ui`.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 418bf6f8-212b-4bb0-a7a5-8231a061da4e
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 3fb69144-fc09-46cf-8560-9b4bc828c60f
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/9f85e954-647c-46a5-90a7-396e495a805a/418bf6f8-212b-4bb0-a7a5-8231a061da4e/sPDHkg8
Replit-Helium-Checkpoint-Created: true

artifacts/api-server/src/routes/index.ts

@@ -4,6 +4,7 @@ import jobsRouter from "./jobs.js";
 import demoRouter from "./demo.js";
 import devRouter from "./dev.js";
 import testkitRouter from "./testkit.js";
+import uiRouter from "./ui.js";
 
 const router: IRouter = Router();
 
@@ -11,6 +12,7 @@ router.use(healthRouter);
 router.use(jobsRouter);
 router.use(demoRouter);
 router.use(testkitRouter);
+router.use(uiRouter);
 
 if (process.env.NODE_ENV !== "production") {
   router.use(devRouter);