Update header and footer on Stacks landing page

[andrewjbtw]

The stacks.stanford.edu landing page lacks a header and is using an old footer. I think we now have a standard header and footer that can be applied to this page, but this will need DLUX review. This is not urgent but I want to have an issue posted for the future.

This ticket supersedes an earlier one about the footer #1039, which I'm going to close. Also, in the time since that ticket was filed in fall 2023, I've taken on PO responsibilities for this page. There had been prior discussions of whether to have a Stacks landing page at all, but after checking with stakeholders (including DLSS Direct), we need to keep it.

[andrewjbtw]

Fixed by #1242