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.

DESCRIPTION

@@ -8,7 +8,8 @@ Authors@R:
 Description: Provides a complete ggplot2 brand theme system for Civilytics
     Consulting LLC, including editorial light, dark, and slide-optimized themes;
     10 curated color palettes for qualitative, sequential, and diverging data;
-    logo composition utilities; and data-wrangling helpers for public-sector
+    logo composition utilities; Quarto themes for HTML reports, PDF, Typst, and
+    Reveal.js presentations; and data-wrangling helpers for public-sector
     analysis.
 License: LGPL (>= 3)
 URL: https://gitea.civilytics.org/Civilytics/civilyticsR
@@ -28,7 +29,8 @@ Imports:
 Encoding: UTF-8
 Suggests:
     testthat (>= 3.0.0),
-    tidycensus
+    tidycensus,
+    quarto
 Config/testthat/edition: 3
 Config/roxygen2/version: 8.0.0
 RoxygenNote: 7.3.3