Redesign: foundations (fonts, colours, header, footer, 404) #29

Part of the redesign build (parent issue linked in the sidebar). Targets the redesign branch.

Set up what every page of the new design uses.

• Fonts, self-hosted, no Google Fonts. Newsreader (regular and italic) for the text of articles and About. DejaVu Sans Mono for everything else: the prototype was designed in Menlo, which is derived from DejaVu Sans Mono, so they look nearly the same and DejaVu works on every system. Subset both.
• Colours. Page #ffffff, ink #151515, muted #686862, line #e5e5e2, panel #f3f3f0, tint #fff9f4, accent #b64b00 (AA on white). Links in running text are underlined.
• Layout. Content up to 1240px wide with 24px side padding.
• Header. 84px tall with a 1px line under it. The wordmark "meaningfool." (22px, -0.055em, the dot in the accent colour) links to the home. On the right, the nav: Home, About (13px, muted). The current page is in ink, underlined in the accent colour with a 6px offset. The nav stays visible on phones.
• Footer. The wordmark at 16px, then About, LinkedIn, GitHub, X (12px, muted).
• Remove Space Mono, Roboto Mono and Poppins, and the weight-300 body text.
• Style the 404 page with the new header and footer.

Done when the preview shows the new header, footer and fonts on every page and makes no request to Google Fonts.