add legend manually to facet gridded ggplot2

I made a facet gridded figure and have changed the background color of the facet strips to match specific groups. In this example those specific groups are where a car manufacturer is located (i.e., Mercedes and Fiat = Europe and Toyota = Japan). How can I add a legend to the facet gridded plot to indicate that the orange fill color means Europe and blue means Japan?

The ideal output would have a legend above the plot with an orange and blue box that says Europe and Japan next to it, respectively.

library(tidyverse)
library(ggh4x)

# Get car make from mtcars and subset
dat <- mtcars |> 
  mutate(
    vehicle = rownames(mtcars)
  ) |> 
  separate(
    col = vehicle,
    into = c('make', 'trash'),
    sep = ' '
  ) |> 
  filter(make %in% c('Merc', 'Fiat', 'Toyota')) |> 
  select(make, mpg, cyl) |> 
  relocate(make)

# facet_grid fill colors based on car make
make_cols <- c(
  Merc = "orange",
  Fiat = "orange",
  Toyota = "dodgerblue"
)

# make figure
dat |> 
  pivot_longer(
    cols = 2:3,
    names_to = 'variable',
    values_to = 'value'
  ) |> 
  ggplot(aes(x = make, y = value)) +
  geom_point() +
  labs(x = NULL,
       y = NULL) +
  theme_bw(base_size = 18) +
  theme(
    strip.background.y = element_rect(fill = 'white'),
    axis.text.x = element_blank()
  ) +
  ggh4x::facet_grid2(
    rows = vars(variable),
    cols = vars(make),
    strip = ggh4x::strip_themed(
      background_x = ggh4x::elem_list_rect(
        fill = make_cols
      )
    )
  )

^{Created on 2025-08-14 with reprex v2.1.1}

One option would be to fake a legend using an unused aesthetic, e.g. I use fill:

library(tidyverse)
library(ggh4x)

# make figure
p <- dat |>
  pivot_longer(
    cols = 2:3,
    names_to = "variable",
    values_to = "value"
  ) |>
  ggplot(aes(x = make, y = value)) +
  geom_point() +
  labs(
    x = NULL,
    y = NULL
  ) +
  theme_bw(base_size = 18) +
  theme(
    strip.background.y = element_rect(fill = "white"),
    axis.text.x = element_blank()
  ) +
  ggh4x::facet_grid2(
    rows = vars(variable),
    cols = vars(make),
    strip = ggh4x::strip_themed(
      background_x = ggh4x::elem_list_rect(
        fill = make_cols
      )
    )
  )

p +
  geom_point(
    aes(fill = make %in% c("Fiat", "Merc")),
    x = NA, y = NA,
    na.rm = TRUE,
    key_glyph = "rect"
  ) +
  scale_fill_manual(
    values = c("dodgerblue", "orange"),
    labels = c("Japan", "Europe"),
    name = NULL,
    guide = guide_legend(reverse = TRUE)
  ) +
  theme(
    legend.position = "top"
  )