feat: add Quarto themes and templates (revealjs, HTML, PDF, Typst)

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.

man/use_civilytics_theme.Rd

@@ -0,0 +1,26 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/quarto.R
+\name{use_civilytics_theme}
+\alias{use_civilytics_theme}
+\title{Install the Civilytics document theme}
+\usage{
+use_civilytics_theme(path = ".", force = FALSE)
+}
+\arguments{
+\item{path}{Character. Project directory to install into. Default `"."`.}
+
+\item{force}{Logical. Overwrite existing files? Default `FALSE`.}
+}
+\value{
+Invisible `NULL`.
+}
+\description{
+Copies Civilytics HTML, PDF (LaTeX), and Typst theme files into
+your Quarto project.  Also installs `_brand.yml` and the logo
+assets it references.
+}
+\examples{
+\dontrun{
+use_civilytics_theme()
+}
+}