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.

R/civilytics-package.R

@@ -1,14 +1,33 @@
-#' @keywords internal
-#' @importFrom stats qbeta
-#' @importFrom stats qnorm
-"_PACKAGE"
-
-## usethis namespace: start
-## usethis namespace: end
-NULL
-
-# state.abb and state.name are lazy data from the datasets package (base R).
-# They cannot be imported via @importFrom — suppress the R CMD check NOTE here.
-utils::globalVariables(c("state.abb", "state.name"))
-
-
+#' @description
+#' 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
+#' }
+#'
+#' @keywords internal
+#' @importFrom stats qbeta
+#' @importFrom stats qnorm
+"_PACKAGE"
+
+## usethis namespace: start
+## usethis namespace: end
+NULL
+
+# state.abb and state.name are lazy data from the datasets package (base R).
+# They cannot be imported via @importFrom -- suppress the R CMD check NOTE here.
+utils::globalVariables(c("state.abb", "state.name"))