Integrate Civilytics Reveal.js slide extension, HTML/PDF/Typst document
themes, and _brand.yml into the package under inst/quarto/. Three new
helper functions (use_civilytics_revealjs, use_civilytics_theme,
use_civilytics_brand) copy assets into a user's Quarto project. Logos
are stored once in inst/img/ and distributed at install time.
