fix: menu items and footer links are scrolling to top

Using button instead of a will prevent the scroll to top issues.

The navbar and footer were made using a at first without an href for simplicity (and the browser does not interpret anchors without href as links). However, you can't tab onto a's without href (even with tabindex). So, I had to reintroduce href.

This patch swaps a with button, which is what I should have done from the start.