Add anchor links to /foundation/working-groups/

It should be possible to link to a specific working group.

Update: while this now possible, e.g. https://matrix.org/foundation/working-groups/#website-and-content, it is missing UI to do so. It should match the other pages.

Start by inspecting the /foundation/working-groups/ page and compare its existing anchor-link behavior with the other pages referenced in the issue. Add matching UI for linking to a specific working group, then verify that the control appears and produces usable links such as #website-and-content.

Written by the indexing model from the issue text.