Routing pattern not included in /message endpoint when using SSE Server

When you set a routing pattern like ...

`app.MapMcp("mymcpserver")`

The endpoint works with  /mymcpserver/sse but this return 

```
event: endpoint
data: /message?sessionId=XXX
```

should be

```
event: endpoint
data: {routing_pattern}/message?sessionId=XXX
```

In my example should be

```
event: endpoint
data: /mymcpserver/message?sessionId=XXX
```