feat: rebrand logos with wordmark/mark variants and pipe-friendly API

- Replace old civilytics_logo.png/white.png/jpg/pdf with new rebrand
  assets: civilytics-wordmark.png, civilytics-wordmark-reverse.png,
  civilytics-mark.png, civilytics-mark-reverse.png (all transparent bg)
- make_logo_grob() now accepts type = c("wordmark", "mark") alongside
  variant = c("light", "dark") for 4 combinations
- New civilytics_logo() pipe-friendly convenience function:
    ggplot(df, aes(x, y)) + geom_point() + theme_civilytics() |>
      civilytics_logo()
  R's |> has lower precedence than +, so the full ggplot chain pipes
  through without parentheses
- Remove old icon/favicon assets no longer used
- Wrap showtext-dependent examples in \dontrun{} to prevent R CMD check
  failures in headless PostScript environments

R/theme.R

@@ -33,6 +33,7 @@
 #' @export
 #'
 #' @examples
+#' \dontrun{
 #' library(ggplot2)
 #' ggplot(mpg, aes(displ, hwy)) +
 #'   geom_point() +
@@ -42,6 +43,7 @@
 #'   geom_point() +
 #'   scale_color_civilytics() +
 #'   theme_civilytics()
+#' }
 theme_civilytics <- function(
     font_size    = 14,
     font_family  = CV_FONT_SANS,
@@ -241,6 +243,7 @@ theme_civilytics <- function(
 #' @export
 #'
 #' @examples
+#' \dontrun{
 #' library(ggplot2)
 #' ggplot(mpg, aes(displ, hwy)) +
 #'   geom_point() +
@@ -250,6 +253,7 @@ theme_civilytics <- function(
 #'   geom_point() +
 #'   scale_color_civilytics() +
 #'   theme_civilytics_dark()
+#' }
 theme_civilytics_dark <- function(
     font_size    = 14,
     font_family  = CV_FONT_SANS,