Dark mode support for django/views/templates/*.html

[Emme Bravo]

Django’s directory_index view uses simple HTML to display a list of files (see ​demo/directory_index). It would be helpful if this was displayed in a dark theme when the user’s operating system is configured to use one, just like the Django admin.

This can be achieved with the color-scheme meta tag, which will tell the browser the page is ready to adapt based on the user’s operating system preferences:

<meta name="color-scheme" content="light dark" />

[Sarah Boyce]

It sounds like there's a request to support dark mode in places other than the admin, including the ​congrats page
Accepting on the grounds that I believe this has accessibility benefits and discussed with Thibaud, cc-ing to confirm.

I'd like to increase the scope of this ticket to all templates in django/views/templates. Each one can be worked on separately with Refs #35875 -- but don't think we need to keep creating new tickets for each one.

[Jacob Walls <jacobtylerwalls@…>]

In 8a0315fa:

Refs #35875 -- Added dark mode support in additional views.

Thanks Thibaud Colas for the review.

[Jacob Walls]

Still need to implement dark theme on the error views (404, 500) to call this done.