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

man/civilytics_logo.Rd

@@ -0,0 +1,63 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/logo.R
+\name{civilytics_logo}
+\alias{civilytics_logo}
+\title{Add a Civilytics logo to a ggplot (pipe-friendly)}
+\usage{
+civilytics_logo(
+  plot,
+  type = c("wordmark", "mark"),
+  variant = c("light", "dark"),
+  margin_param = NULL
+)
+}
+\arguments{
+\item{plot}{A ggplot object.}
+
+\item{type}{Character. `"wordmark"` (default) or `"mark"`. Passed to
+[make_logo_grob()].}
+
+\item{variant}{Character. `"light"` (default) or `"dark"`. Passed to
+[make_logo_grob()].}
+
+\item{margin_param}{Numeric or `NULL`. Manual margin adjustment passed to
+[add_logo()].}
+}
+\value{
+A grob (from [gridExtra::arrangeGrob()]) ready to draw with
+  [grid::grid.draw()].
+}
+\description{
+A convenience wrapper that creates the logo grob and attaches it below the
+plot in one call. Designed for use with the base pipe `|>`:
+}
+\details{
+```
+ggplot(mpg, aes(displ, hwy)) +
+  geom_point() +
+  theme_civilytics() |>
+  civilytics_logo()
+```
+
+Since `|>` has lower precedence than `+`, the entire ggplot chain is piped
+as the first argument — no parentheses needed.
+}
+\examples{
+\dontrun{
+library(ggplot2); library(grid)
+
+# Pipe-friendly usage
+ggplot(mpg, aes(displ, hwy)) +
+  geom_point() +
+  theme_civilytics() |>
+  civilytics_logo() |>
+  grid.draw()
+
+# Dark theme with mark
+ggplot(mpg, aes(displ, hwy)) +
+  geom_point() +
+  theme_civilytics_dark() |>
+  civilytics_logo(variant = "dark", type = "mark") |>
+  grid.draw()
+}
+}