Configure header/nav component built in DCAR as an atom

[petternitter]

Related to #15868, theguardian.com/football/world-cup-2026/overview is rendered in frontend. As such, the header/nav component built in DCAR (#15704) won't appear on this page - but this page is linked to from the nav (Match centre) and needs to feature the nav to complete the user journey.

Longer-term, we should rebuild the /overview page in DCAR - however, as a workaround for this tournament, we should configure the header/nav component built in DCAR in a way that makes it available as an atom we can insert as a trasher.

This effectively is the same approach we are taking for #15753 (the match day atom) where we are building it in DCAR but making it available as an atom by "wrapping" it as such.

[petternitter]

@marjisound Just to clarify: we don't need to consider the app for this, as Harry has built a header/nav trasher for the app (PR here: https://github.com/guardian/interactives/pull/3144)

Will leave it to you / whoever completes this ticket to decide if it makes sense to build upon what Harry's done for the app to cover the web use case (i.e. hide the header on web so we're only showing the nav + add the World Cup front link in to the nav) so we only have one thrasher to manage, or if it's better to create a separate atom/thrasher for web given the visual differences.

Any questions / anything not clear, just let me know!