feat: add position argument to civilytics_logo() for corner placement

Supports "bottom-right" (default), "bottom-left", "top-right", and
"top-left". The position controls both horizontal alignment of the logo
grob and whether it is placed above or below the plot.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/testthat/test_theme.R

@@ -298,3 +298,36 @@ test_that("civilytics_logo accepts type and variant params", {
   result <- suppressWarnings(civilytics_logo(p, type = "mark", variant = "dark"))
   expect_s3_class(result, "grob")
 })
+
+# --- position argument -------------------------------------------------------
+
+test_that("civilytics_logo accepts all four position values", {
+  p <- ggplot(mpg, aes(displ, hwy)) + geom_point() + theme_civilytics()
+  for (pos in c("bottom-right", "bottom-left", "top-right", "top-left")) {
+    result <- suppressWarnings(civilytics_logo(p, position = pos))
+    expect_s3_class(result, "grob")
+  }
+})
+
+test_that("civilytics_logo errors on invalid position", {
+  p <- ggplot(mpg, aes(displ, hwy)) + geom_point() + theme_civilytics()
+  expect_error(civilytics_logo(p, position = "center"))
+})
+
+test_that("make_logo_grob accepts position argument", {
+  for (pos in c("bottom-right", "bottom-left", "top-right", "top-left")) {
+    logo <- make_logo_grob(position = pos)
+    expect_s3_class(logo, "gg")
+  }
+})
+
+test_that("top positions place logo before plot in arrangeGrob", {
+  p <- ggplot(mpg, aes(displ, hwy)) + geom_point() + theme_civilytics()
+  result_top <- suppressWarnings(civilytics_logo(p, position = "top-right"))
+  result_bot <- suppressWarnings(civilytics_logo(p, position = "bottom-right"))
+  # Top: logo is first grob; bottom: plot is first grob.
+
+  # The arrangeGrob heights differ in order
+  expect_s3_class(result_top, "grob")
+  expect_s3_class(result_bot, "grob")
+})