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.

DESCRIPTION

@@ -1,13 +1,15 @@
 Package: civilytics
 Type: Package
-Title: Utilities Functions for Civilytics
+Title: Brand Themes, Color Palettes, and Utility Functions for Civilytics
 Version: 0.2.0
 Authors@R:
     person("Jared", "E. Knowles", email = "jared@civilytics.com",
            role = c("aut", "cre"))
-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.
+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
+    analysis.
 License: LGPL (>= 3)
 URL: https://gitea.civilytics.org/Civilytics/civilyticsR
 BugReports: https://gitea.civilytics.org/Civilytics/civilyticsR/issues