top level atom rel-alternate: use rel-self or input URL instead of h-card u-url?

thanks for suggesting, @gregorlove!

example, https://granary.io/url?input=html&output=atom&url=https://gregorlove.com/notes/ includes:

```xml
<link rel="alternate" href="https://gregorlove.com/" type="text/html" />
```

the input URL, https://gregorlove.com/notes/ , has rel-self pointing to itself.