Usage of deprecated `A2AExpressApp` in the JS examples

### What happened?

The `samples/js` samples uses the `A2AExpressApp` which is now deprecated
```
// 4. Create and setup A2AExpressApp
const appBuilder = new A2AExpressApp(requestHandler);
const expressApp = appBuilder.setupRoutes(express());
```

The hint is to use:
```
Deprecated:
Use specific middlewares (jsonRpcHandler, agentCardHandler) directly.
```

TODO:
The examples should be updated to align with the newest package version `v0.3.7`.

### Relevant log output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct