feat: improved page layout/template

[isobelmcrae]

currently we do not have back buttons/title bar on pages. i think we should change the base layout (base.njk) to a page layout, which we then add a title bar to

todos:

• title bar on page, to navigate to home/back button
• table of contents
• fix layout of footnotes (make them not center aligned)
• improve author layout on mobile (condensed view if it wraps?)