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/dot-copy_pkg_file.Rd

@@ -0,0 +1,24 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/quarto.R
+\name{.copy_pkg_file}
+\alias{.copy_pkg_file}
+\title{Copy a package file to a project directory}
+\usage{
+.copy_pkg_file(src, dst, path, force)
+}
+\arguments{
+\item{src}{Relative path within the installed package (under `inst/`).}
+
+\item{dst}{Destination path relative to `path`.}
+
+\item{path}{Project root.}
+
+\item{force}{Overwrite existing files?}
+}
+\value{
+Invisible logical indicating success.
+}
+\description{
+Copy a package file to a project directory
+}
+\keyword{internal}