`omarchy region china` switches the system language to zh_CN, installs the
Rime Ice input method through Andy Stewart's rime-ice-installer, makes Rime
the default with Ctrl+Space as the toggle, and swaps the Omarchy menu to
Chinese labels through the user-extension overlay; `omarchy region world`
puts the language and menu back and leaves the input method installed.
mergeMenuSources now only overrides the fields an extension declares, as
docs/menu.md documents, which the label-only overlay needs.
Co-authored-by: Andy Stewart <lazycat.manatee@gmail.com>