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.

R/theme.R

@@ -24,7 +24,8 @@
 #' @param rel_tiny Numeric. Scale factor for tiny text relative to `font_size`.
 #'   Default `11/14`.
 #' @param rel_large Numeric. Scale factor for large text (titles) relative to
-#'   `font_size`. Default `16/14`.
+#'   `font_size`. Default `20/14` (~1.43x), matching the Civilytics editorial
+#'   design system.
 #' @param ink Character. Hex code for foreground/text color. Defaults to
 #'   [civilytics_colors]`["ink"]` (`#0E1A2B`).
 #' @param paper Character. Hex code for background color. Defaults to
@@ -40,6 +41,26 @@
 #'   transparent background (useful for slides or overlay on colored
 #'   surfaces).
 #'
+#' @section Font size hierarchy:
+#' All text sizes are derived from `font_size` using relative scale factors.
+#' At the default `font_size = 14`:
+#'
+#' | Element | Scale factor | Default size |
+#' |:--------|:-------------|:-------------|
+#' | Plot title | `rel_large` (1.43x) | ~20 pt |
+#' | Subtitle | 1.0x | 14 pt |
+#' | Axis text (tick labels) | `rel_small` (0.86x) | ~12 pt |
+#' | Axis titles | `rel_small` (0.86x) | ~12 pt |
+#' | Legend text | `rel_small` (0.86x) | ~12 pt |
+#' | Caption | `rel_tiny` (0.79x) | ~11 pt |
+#' | Legend title | `rel_tiny` (0.79x) | ~11 pt |
+#' | Strip text (facets) | `rel_small` (0.86x) | ~12 pt |
+#'
+#' To uniformly scale all text, change `font_size`. To adjust only the title
+#' prominence, change `rel_large`. When using [civilytics_logo()] to add a
+#' logo below the plot, pass `font_scale` to compensate for viewport
+#' shrinkage.
+#'
 #' @return A complete ggplot2 [ggplot2::theme()] object.
 #' @export
 #'
@@ -62,6 +83,11 @@
 #' ggplot(mpg, aes(displ, hwy)) +
 #'   geom_point() +
 #'   theme_civilytics(paper_bg = FALSE)
+#'
+#' # Larger text for poster or display
+#' ggplot(mpg, aes(displ, hwy)) +
+#'   geom_point() +
+#'   theme_civilytics(font_size = 18)
 #' }
 theme_civilytics <- function(
     font_size    = 14,
@@ -70,7 +96,7 @@ theme_civilytics <- function(
     line_size    = 0.5,
     rel_small    = 12 / 14,
     rel_tiny     = 11 / 14,
-    rel_large    = 16 / 14,
+    rel_large    = 20 / 14,
     ink          = unname(civilytics_colors["ink"]),
     paper        = unname(civilytics_colors["paper"]),
     accent       = unname(civilytics_colors["ember_600"]),
@@ -132,7 +158,7 @@ theme_civilytics <- function(
       axis.line.y = ggplot2::element_blank(),
       axis.text = ggplot2::element_text(
         color = ink_2,
-        size  = small_size
+        size  = ggplot2::rel(rel_small)
       ),
       axis.text.x = ggplot2::element_text(
         margin = ggplot2::margin(t = small_size / 4),
@@ -249,7 +275,7 @@ theme_civilytics <- function(
       ),
       plot.title.position = "plot",
       plot.subtitle = ggplot2::element_text(
-        size       = ggplot2::rel(rel_small),
+        size       = ggplot2::rel(1),
         color      = ink_2,
         hjust      = 0,
         vjust      = 1,
@@ -307,7 +333,7 @@ theme_civilytics_dark <- function(
     line_size    = 0.5,
     rel_small    = 12 / 14,
     rel_tiny     = 11 / 14,
-    rel_large    = 16 / 14,
+    rel_large    = 20 / 14,
     ink          = unname(civilytics_colors["paper"]),
     paper        = unname(civilytics_colors["navy_700"]),
     accent       = unname(civilytics_colors["ember_400"]),
@@ -359,7 +385,7 @@ theme_civilytics_slide <- function(
     line_size    = 0.5,
     rel_small    = 12 / 14,
     rel_tiny     = 11 / 14,
-    rel_large    = 16 / 14,
+    rel_large    = 20 / 14,
     ink          = unname(civilytics_colors["ink"]),
     paper        = unname(civilytics_colors["paper"]),
     accent       = unname(civilytics_colors["ember_600"]),