Set device appearance as the default for chromium

So we will be switching correctly from light/dark mode depending on the
theme.

install/config/theme.sh

@@ -22,3 +22,6 @@ sudo chmod a+rw /etc/chromium/policies/managed
 
 sudo mkdir -p /etc/brave/policies/managed
 sudo chmod a+rw /etc/brave/policies/managed
+
+# Default Chromium to follow system appearance ("device") instead of dark
+echo '{"browser":{"theme":{"color_scheme":0}}}' | sudo tee /usr/lib/chromium/initial_preferences >/dev/null