feat: expand color system to 53 colors/10 palettes, add grid/slide themes, and README gallery

Replace the 16-color / 3-palette system with the full Civilytics design
system: 53 named colors (full navy, ember, violet ramps plus teal, plum,
moss, brass supporting hues) and 10 visualization palettes (qual,
qual_warm, qual_cool, seq_ember, seq_navy, seq_violet, seq_paper_ink,
div_navy_ember, div_violet_ember).

Enrich theme_civilytics() with grid and paper_bg parameters, add
theme_civilytics_slide() for presentations, and load all four brand fonts
(Inter, Libre Franklin, Source Serif 4, JetBrains Mono).

Add README.Rmd with rendered gallery showing all palettes, theme
variants, grid options, dark/slide modes, facets, and scale usage.

man/civilytics-package.Rd

@@ -4,10 +4,32 @@
 \name{civilytics-package}
 \alias{civilytics}
 \alias{civilytics-package}
-\title{civilytics: Utilities Functions for Civilytics}
+\title{civilytics: Brand Themes, Color Palettes, and Utility Functions for Civilytics}
 \description{
-House R functions for Civilytics Consulting LLC. This package implements a variety of useful functions for creating and branding analyses produced by Civilytics Consulting LLC.
+Provides a complete ggplot2 brand theme system for Civilytics Consulting,
+including editorial light, dark, and slide-optimized themes; 10 curated
+color palettes; logo composition; and data-wrangling helpers for
+public-sector analysis.
 }
+\section{Themes}{
+
+\itemize{
+  \item [theme_civilytics()] -- editorial theme with warm paper background
+  \item [theme_civilytics_dark()] -- navy background variant
+  \item [theme_civilytics_slide()] -- transparent background, larger text
+}
+}
+
+\section{Color palettes}{
+
+\itemize{
+  \item [civilytics_colors] -- 53 named brand colors
+  \item [civilytics_palettes] -- 10 visualization palettes
+  \item [civilytics_palette()] -- extract colors by palette name
+  \item [scale_color_civilytics()] / [scale_fill_civilytics()] -- ggplot2 scales
+}
+}
+
 \seealso{
 Useful links:
 \itemize{