feat: bump title sizes, add font_scale to logo functions, ship SVGs

- Change rel_large default from 16/14 to 20/14 (~1.43x) to match the
  Civilytics editorial design system. Subtitle now renders at 1.0x base
  instead of 0.86x.
- Switch axis.text to rel() sizing so all text elements cascade from the
  root font_size, enabling uniform scaling.
- Add font_scale parameter (default 1.1) to civilytics_logo(),
  add_logo(), and add_logo_ga() — inflates text by ~10% before
  arrangeGrob composition to compensate for viewport shrinkage.
- Ship SVG logo variants (mark, wordmark, pulse) in inst/img/ for
  Quarto/HTML templates.
- Add "Maintaining brand assets" section to README documenting inst/img/
  file inventory and update workflow.
- Document full font size hierarchy in theme_civilytics() roxygen.

man/add_logo.Rd

@@ -4,7 +4,7 @@
 \alias{add_logo}
 \title{Add a logo to a ggplot2 object}
 \usage{
-add_logo(plot, logo, margin_param = NULL)
+add_logo(plot, logo, margin_param = NULL, font_scale = 1.1)
 }
 \arguments{
 \item{plot}{a ggplot2 grob}
@@ -12,6 +12,11 @@ add_logo(plot, logo, margin_param = NULL)
 \item{logo}{a logo grob created by make_logo_grob()}
 
 \item{margin_param}{a numeric specifying what margin to add or subtract to align the logo}
+
+\item{font_scale}{Numeric. Multiplicative scaling factor applied to text
+sizes before composing the plot with the logo. Default `1.1` inflates
+text by ~10 \% to compensate for the viewport shrinkage caused by
+[gridExtra::arrangeGrob()]. Set to `1` to disable.}
 }
 \value{
 a grob with a logo attached to it ready to plot