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

NAMESPACE

@@ -3,6 +3,9 @@
 export(add_logo)
 export(add_logo_ga)
 export(agresti_coull_interval)
+export(civilytics_colors)
+export(civilytics_load_fonts)
+export(civilytics_pal)
 export(clopper_pearson)
 export(countCleanr)
 export(countDots)
@@ -32,15 +35,21 @@ export(rnh)
 export(round_to_nearest_half)
 export(safe_max)
 export(safe_ratio)
+export(scale_color_civilytics)
+export(scale_fill_civilytics)
 export(simpleCap)
 export(star_subs)
 export(theme_civilytics)
+export(theme_civilytics_dark)
 export(trim_max)
 export(waldInterval)
 export(z_gap_test)
 export(z_univariate)
 import(ggplot2)
+importFrom(ggplot2,annotation_custom)
+importFrom(ggplot2,ggplot)
 importFrom(ggplot2,theme)
+importFrom(ggplot2,theme_void)
 importFrom(graphics,rasterImage)
 importFrom(grid,grid.draw)
 importFrom(grid,rasterGrob)