Use json for htmx posts

[Xylon2]

With this extension we can make HTMX post in JSON instead of form-urlencoded: https://github.com/bigskysoftware/htmx-extensions/blob/main/src/json-enc/README.md

And we can send the anti-forgery token as a header with HTMX hx-headers.

Advantages:

• handles lists better