A11y: Interactive controls must not be nested

[ralf401]

As a user with handicap (here: visually impaired or no mouse usage), I want to use Zammad and the new documentation without an issue.

Acceptance criteria

• Interactive controls must not be nested / interactive controls do not contain focusable child elements.

Additional information

Check with AxeTools:

Explanation:

https://dequeuniversity.com/rules/axe/4.10/nested-interactive?application=AxeFirefox

Upstream documentation issue/PR:

• accessibility: interactive controls should not be nested vuejs/vitepress#3517
• sidebar uses native <details> for collapsible groups [#3804. also #3517] vuejs/vitepress#3806

This issue was for the new docs in the first place, but it should get fixed in Zammad as well (even though Axe DevTools don't complain about this issue). Probably the navigation tabs with the close icon are affected as well.