The URL input in the link edition picker is not keyboard focusable

Claude Code helped me find a cause for this difference in behaviour:
Selectize.js `setup()` method read the HTML attribute to store the tabindex of the input.
Then it restores this stored tabindex in `destroy()` and does not add the attribute back if the value is empty.
Tom select's constructor reads the DOM properties and saves those in its `setup()`.
Then its `destroy()` writes it back as a property, and uses `0` as a default value.

TLDR: This is a simple without any tabindex, selectize defaulted to not include the tabindex if it wasn't there, Tom select defaults to `tabindex="0"` when it's not there. IMO selectize solution was better but we need to find a working solution for us with tom select.