Extracts the avatar components and the style tokens into shared/ui, which
both apps consume as a workspace package, to try out ADR 2. Nix and the
Docker setups are not updated yet.
When users block web fonts, code was rendered in the browser's default
sans-serif font because the JetBrains Mono code font tokens had no
generic fallback. Add `monospace` as a fallback so code stays
monospaced.
Fixes: 8942cea33a