Navigation on working group pages looks like a ToC

[simon-friedberger]

Describe the issue
Working groups have multiple pages. These can be reached via a menu. Most working groups have a default page called "Summary". This makes the menu look like a ToC:

On small screens the menu starts off collapsed and hidden behind a "Toggle content" which also suggests that it might be a ToC and not a navigation.

To reproduce
Visit any working group page and try to find the email archive.

Expected behavior
It should be visually clear that there are multiple pages. Maybe "Toggle content" should be called "Navigation". Maybe there should be a header called "Navigation".

[koalie]

@vivienlacourba in the CMS, the right-hand side navigation is called "In this section". In the group pages it's called "Summary". If we wanted to harmonize, "Summary" should be replaced by "In this section".
But I am not against "Navigation" as suggested above, if you wanted to keep to non-harmonized language.