feat: add brand color system, showtext fonts, and dark theme

- R/colors.R: civilytics_colors named vector (from --cv-* CSS vars on
  civilytics.com), three palettes (main/sequential/diverging),
  scale_color_civilytics() and scale_fill_civilytics() for ggplot2
- R/fonts.R: auto-loads Inter + Libre Franklin from Google Fonts via
  showtext in .onLoad(); exports civilytics_load_fonts() for manual retry
- R/theme.R: wires ggplot2 4.0 ink/paper/accent params into theme_grey()
  base, adds title_family + strip_color params; new theme_civilytics_dark()
  using navy_dark background and warm off-white text
- R/logo.R: make_logo_grob(variant) accepts "light"/"dark" to select the
  white logo for dark-background compositions
- DESCRIPTION: adds showtext, sysfonts; pins ggplot2 >= 4.0.0
- tests/testthat/test_theme.R: full test suite for colors, palettes,
  scales, both theme variants, and logo grob variants

man/theme_civilytics.Rd

@@ -2,33 +2,75 @@
 % Please edit documentation in R/theme.R
 \name{theme_civilytics}
 \alias{theme_civilytics}
-\title{Make the Civilytics plot theme}
+\title{Civilytics ggplot2 theme}
 \usage{
 theme_civilytics(
   font_size = 14,
-  font_family = "",
+  font_family = CV_FONT_SANS,
+  title_family = CV_FONT_DISPLAY,
   line_size = 0.5,
   rel_small = 12/14,
   rel_tiny = 11/14,
-  rel_large = 16/14
+  rel_large = 16/14,
+  ink = unname(civilytics_colors["ink"]),
+  paper = unname(civilytics_colors["paper"]),
+  accent = unname(civilytics_colors["accent"]),
+  strip_color = unname(civilytics_colors["paper_2"])
 )
 }
 \arguments{
-\item{font_size}{default 14, a number representing the base font for the theme}
+\item{font_size}{Numeric. Base font size in points. Default `14`.}
 
-\item{font_family}{default "", a character for the font family to use in the theme}
+\item{font_family}{Character. Font family for body/axis text. Default
+`"Inter"` (loaded via showtext).}
 
-\item{line_size}{default 0.5, the line size to use for the theme}
+\item{title_family}{Character. Font family for plot titles and strip labels.
+Default `"Libre Franklin"` (loaded via showtext).}
 
-\item{rel_small}{default 12/14, the scale factor to create a small font from the base font_size}
+\item{line_size}{Numeric. Base line width. Default `0.5`.}
 
-\item{rel_tiny}{default 11/14, the scale factor to create a tiny font from the base font_size}
+\item{rel_small}{Numeric. Scale factor for small text relative to
+`font_size`. Default `12/14`.}
 
-\item{rel_large}{default 16/14, the scale factor to create a large font from the base font_size}
+\item{rel_tiny}{Numeric. Scale factor for tiny text relative to `font_size`.
+Default `11/14`.}
+
+\item{rel_large}{Numeric. Scale factor for large text (titles) relative to
+`font_size`. Default `16/14`.}
+
+\item{ink}{Character. Hex code for foreground/text color. Defaults to
+[civilytics_colors]`["ink"]` (`#0E1A2B`).}
+
+\item{paper}{Character. Hex code for background color. Defaults to
+[civilytics_colors]`["paper"]` (`#FAF7F2`).}
+
+\item{accent}{Character. Hex code for accent/highlight color. Defaults to
+[civilytics_colors]`["accent"]` (`#C25311`).}
+
+\item{strip_color}{Character. Hex code for facet strip background. Defaults
+to [civilytics_colors]`["paper_2"]` (`#F2EDE4`).}
 }
 \value{
-a ggplot2 theme object suitable for combining with ggplot objects to theme them
+A complete ggplot2 [ggplot2::theme()] object.
 }
 \description{
-Make the Civilytics plot theme
+A complete ggplot2 theme built on [ggplot2::theme_grey()] using the
+Civilytics brand color palette and typography. Requires ggplot2 >= 4.0.0
+for the `ink`, `paper`, and `accent` base-theme parameters.
+}
+\details{
+Brand fonts (Inter for UI text, Libre Franklin for titles) are loaded
+automatically via [showtext] when the package is attached. Call
+[civilytics_load_fonts()] to reload them if needed.
+}
+\examples{
+library(ggplot2)
+ggplot(mpg, aes(displ, hwy)) +
+  geom_point() +
+  theme_civilytics()
+
+ggplot(mpg, aes(displ, hwy, colour = class)) +
+  geom_point() +
+  scale_color_civilytics() +
+  theme_civilytics()
 }