feat(flextable): add reusable Civilytics flextable branding helpers

Generalize the flextable brand styling and "export to PNG + stamp logo"
pattern repeated across Civilytics projects into two small functions:

- style_flextable_civilytics(): applies only the visual brand (header
  fill/color, body font/size, zebra striping guarded for <2 rows,
  borders, footer styling, fixed layout) to an already-structured
  flextable. Every value is an overridable parameter; zebra toggles
  striping. Structure (labels, headers, widths, alignment, footer text)
  stays with the caller.
- save_branded_flextable_png(): exports a styled flextable to PNG via
  ragg::agg_png() sized to the table plus extra_height headroom, then
  optionally stamps the logo via stamp_logo_png() (... forwarded).

flextable, officer, and ragg are added to Suggests (not Imports) to keep
the base install light; both functions reference them fully qualified and
guard with requireNamespace() + an install hint. Real round-trip tests
cover styling, 1-row idempotence, PNG export, and extra_height.

man/save_branded_flextable_png.Rd

@@ -0,0 +1,62 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/flextable.R
+\name{save_branded_flextable_png}
+\alias{save_branded_flextable_png}
+\title{Save a branded flextable to a logo-stamped PNG}
+\usage{
+save_branded_flextable_png(
+  ft,
+  path,
+  logo = TRUE,
+  res = 300,
+  extra_height = 0.4,
+  ...
+)
+}
+\arguments{
+\item{ft}{A [flextable::flextable()] object, typically already styled with
+[style_flextable_civilytics()].}
+
+\item{path}{Character. Output PNG path. Returned invisibly.}
+
+\item{logo}{Logical. Stamp the Civilytics logo onto the saved PNG via
+[stamp_logo_png()]. Default `TRUE`.}
+
+\item{res}{Numeric. Output resolution in PPI passed to [ragg::agg_png()].
+Default `300`.}
+
+\item{extra_height}{Numeric. Additional height in inches added to the
+table's natural height to leave room for the stamped logo. Default `0.4`.}
+
+\item{...}{Additional arguments forwarded to [stamp_logo_png()] (e.g.
+`type`, `variant`, `position`, `width_frac`, `margin_frac`).}
+}
+\value{
+`path`, invisibly.
+}
+\description{
+Exports a styled [flextable::flextable()] to a PNG via
+[ragg::agg_png()] (sized to the table's own dimensions plus a little
+headroom for the logo), then optionally stamps the Civilytics logo onto the
+file with [stamp_logo_png()] so file-based tables stay visually consistent
+with [civilytics_logo()]-branded plots.
+}
+\details{
+`ragg` and `flextable` are Suggested (not Imported); this function errors
+with an install hint if either is unavailable.
+}
+\examples{
+\dontrun{
+library(flextable)
+ft <- flextable(head(mtcars)) |>
+  add_footer_lines("Source: mtcars") |>
+  style_flextable_civilytics()
+save_branded_flextable_png(ft, "table.png")
+save_branded_flextable_png(ft, "table.png", position = "bottom-left")
+knitr::include_graphics("table.png")
+}
+}
+\seealso{
+[style_flextable_civilytics()] to apply the brand styling, and
+  [stamp_logo_png()] for the underlying logo compositing.
+}

man/style_flextable_civilytics.Rd

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+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/flextable.R
+\name{style_flextable_civilytics}
+\alias{style_flextable_civilytics}
+\title{Apply the Civilytics brand styling to a flextable}
+\usage{
+style_flextable_civilytics(
+  ft,
+  header_bg = "#2c3e50",
+  header_color = "white",
+  title_fontsize = 14,
+  body_fontsize = 11,
+  font_name = "Arial",
+  zebra = TRUE,
+  zebra_bg = "#f0f0eb",
+  outer_border_color = "#888888",
+  outer_border_width = 1,
+  inner_border_color = "#cccccc",
+  inner_border_width = 0.5,
+  footer_fontsize = 9,
+  footer_color = "#555555"
+)
+}
+\arguments{
+\item{ft}{A [flextable::flextable()] object.}
+
+\item{header_bg}{Character. Header background fill. Default `"#2c3e50"`.}
+
+\item{header_color}{Character. Header text color. Default `"white"`.}
+
+\item{title_fontsize}{Numeric. Font size for the first header line (the
+title row, `i = 1`). Default `14`.}
+
+\item{body_fontsize}{Numeric. Body font size. Default `11`.}
+
+\item{font_name}{Character. Font family applied to all parts. Default
+`"Arial"`.}
+
+\item{zebra}{Logical. Apply alternating-row striping to even body rows.
+Default `TRUE`. Safely skipped for tables with fewer than two body rows.}
+
+\item{zebra_bg}{Character. Fill color for striped (even) body rows.
+Default `"#f0f0eb"`.}
+
+\item{outer_border_color}{Character. Outer border color. Default
+`"#888888"`.}
+
+\item{outer_border_width}{Numeric. Outer border width. Default `1`.}
+
+\item{inner_border_color}{Character. Inner horizontal border color (body).
+Default `"#cccccc"`.}
+
+\item{inner_border_width}{Numeric. Inner horizontal border width. Default
+`0.5`.}
+
+\item{footer_fontsize}{Numeric. Footer font size (applied only if a footer
+part exists). Default `9`.}
+
+\item{footer_color}{Character. Footer text color. Default `"#555555"`.}
+}
+\value{
+The styled [flextable::flextable()] object.
+}
+\description{
+Applies *only* the visual Civilytics brand to an already-structured
+[flextable::flextable()] — header fill and color, body font and size,
+zebra striping, borders, footer styling, and a fixed table layout. The
+caller remains responsible for table *structure*: labels
+([flextable::set_header_labels()]), header/title lines
+([flextable::add_header_lines()]), column widths ([flextable::width()]),
+alignment ([flextable::align()]), and footer text
+([flextable::add_footer_lines()]). This separation keeps styling reusable
+across projects while leaving content decisions where they belong.
+}
+\details{
+`flextable`, `officer`, and `ragg` are Suggested (not Imported) to keep the
+base install light, so this function errors with an install hint if
+`flextable` is unavailable.
+}
+\examples{
+\dontrun{
+library(flextable)
+ft <- flextable(head(mtcars)) |>
+  add_header_lines("Motor Trend Cars") |>
+  add_footer_lines("Source: mtcars") |>
+  style_flextable_civilytics()
+}
+}
+\seealso{
+[save_branded_flextable_png()] to export the styled table to a
+  logo-stamped PNG.
+}