Fix possible unbound variable issue in skeleton

[tomdtp]

Fixes self-referential template issues that showed up with django-fastdev enabled.

Also the regular changelist now follows Django’s own action_form / cl.show_admin_actions contract again, while dataset views get an explicit has_action_form flag so they only show bulk-action UI when actions are actually available.

[lukasvinclav]

Thanks for PR. Can you provide a description how can I replicate the issue so I can test it on local machine? I'm particularly interested in testing unfold_admin_actions.

btw you forget to fill the template questions ;-) Did you used AI to create this code?

[tomdtp]

I separated the 2 issues, so this is now just a fix for the unbound self referencing variables.

To reproduce this you can add django-fastdev to the project and then add FASTDEV_STRICT_TEMPLATE_CHECKING = True to the settings.py. You will then directly see the unbound variable error for is_fullwidth. (if you are on main, from this branch it is fixed) if you are unauthenticated and go to the login page of the django admin.

sorry, I did not see any template questions. I just checked the other open PRs and also couldn't see any templates. so if you have questions please ask away :) I did use AI to review the code change (because I wanted it to doublecheck the default values)

the extracted issue is a contract issue, I will issue a separate pr for it