Align the China region to the official cn profile

The region value is cn, the China files live under default/regions/cn/, and
omarchy-apply-pacman renders pacman for every caller: the .cn twins of the
channel servers first, then .org, USTC and ArchLinuxCN. Switching to China
installs and trusts the ArchLinuxCN keyring. A migration renames china to cn
and repoints the drop-in links.

default/omarchy/omarchy-menu.jsonc

@@ -178,7 +178,7 @@
   "setup.default.editor.emacs": {"icon":" ","label":"Emacs","checked":"[[ \"$(omarchy-default-editor)\" == \"emacs\" ]]","action":"omarchy-default-editor emacs"},
   "setup.region": {"icon":"󰇧","label":"Region"},
   "setup.region.global": {"icon":"󰖟","label":"Global","checked":"[[ \"$(omarchy-region)\" == \"Global\" ]]","action":"omarchy-launch-floating-terminal-with-presentation 'omarchy-region global'"},
-  "setup.region.china": {"icon":"󰈻","label":"China","checked":"[[ \"$(omarchy-region)\" == \"China\" ]]","action":"omarchy-launch-floating-terminal-with-presentation 'omarchy-region china'"},
+  "setup.region.china": {"icon":"󰈻","label":"China","checked":"[[ \"$(omarchy-region)\" == \"China\" ]]","action":"omarchy-launch-floating-terminal-with-presentation 'omarchy-region cn'"},
   "setup.plugin": {"icon":"󰐱","label":"Plugins","aliases":["plugin","plugins"]},
   "setup.plugin.enable": {"icon":"󰄬","label":"Enable Plugin","action":"omarchy-menu-plugin enable"},
   "setup.plugin.disable": {"icon":"󰅖","label":"Disable Plugin","action":"omarchy-menu-plugin disable"},

default/regions/cn/environment.conf

@@ -5,4 +5,4 @@ GOPROXY=https://mirrors.aliyun.com/goproxy/,direct
 RUSTUP_DIST_SERVER=https://mirrors.aliyun.com/rustup
 RUSTUP_UPDATE_ROOT=https://mirrors.aliyun.com/rustup/rustup
 BUNDLE_MIRROR__ALL=https://mirrors.aliyun.com/rubygems/
-MAVEN_ARGS=--global-settings /usr/share/omarchy/default/region/china/maven-settings.xml
+MAVEN_ARGS=--global-settings /usr/share/omarchy/default/regions/cn/maven-settings.xml