Biographical Info field on contributors profile is double-encoded

The Biographical Info (cap-description) field is double encoded. It generates HTML like this:

```
Biographical Info
&Aaron is
here.
```

In `class-coauthors-guest-authors.php`, in `get_guest_author_fields()`, we have this code:

```
array(
'key' => 'description',
'label' => __( 'Biographical Info', 'co-authors-plus' ),
'group' => 'about',
'sanitize_function' => 'wp_filter_post_kses',
),
```

By calling `wp_filter_post_kses` instead of the default filter (`sanitize_text_field`), we end up with the double encoding.

Start in class-coauthors-guest-authors.php at get_guest_author_fields(), focusing on the description field and its sanitize_function. Reproduce the generated Biographical Info textarea HTML and compare it with the expected single-encoded value. Done means the field no longer produces double-encoded content without changing the intended sanitization behavior.

Written by the indexing model from the issue text.