Console error on tv embed page - `site.load` undefined

https://lichess.org/tv/frame?theme=brown&bg=dark

```
Uncaught TypeError: Cannot read properties of undefined (reading 'then')
```

https://github.com/lichess-org/lila/blob/e9e0afd9c4272572f63e100e3193549fddc38536/ui/site/src/dialog.ts#L10