Server-side HEEx syntax highlighting via makeup_eex's HEEx lexer. The lexer is looked up from Makeup's registry by name ("heex"), so we don't hardcode its module. On any lexing error we fall back to HTML-escaped plain text.

Only the token markup is produced here; the colors live in assets/css/app.css (a Flexoki palette with light/dark variants) so they can theme with the page.