Point package managers at China mirrors on cn installs

npm, PyPI and uv, Go, rustup and crates.io, RubyGems and Bundler,
and Maven reach their registries slowly or not at all from China.
On a cn install, link the profile's environment, cargo and gem
drop-ins into place. A regular file the admin wrote is never
replaced; the install fails instead.

install/config/all.sh

@@ -1,3 +1,4 @@
+run_logged "$OMARCHY_INSTALL/config/region.sh"
 run_logged "$OMARCHY_INSTALL/config/theme-system.sh"
 run_logged "$OMARCHY_INSTALL/config/browser-policy.sh"
 run_logged "$OMARCHY_INSTALL/config/increase-lockout-limit.sh"

install/config/region.sh

@@ -0,0 +1,33 @@
+cn_links=(
+  "environment.conf /etc/environment.d/90-omarchy-china.conf"
+  "cargo.toml /.cargo/config.toml"
+  "gemrc /etc/gemrc"
+)
+
+# The installer writes the marker from the timezone.
+region=global
+if [[ -e /etc/omarchy/region ]]; then
+  region=$(</etc/omarchy/region)
+fi
+
+case $region in
+global) ;;
+cn)
+  for link in "${cn_links[@]}"; do
+    read -r _ target <<<"$link"
+    if [[ -e $target && ! -L $target ]]; then
+      echo "Refusing to replace $target, which Omarchy did not create" >&2
+      exit 1
+    fi
+  done
+  for link in "${cn_links[@]}"; do
+    read -r source target <<<"$link"
+    mkdir -p "${target%/*}"
+    ln -sfn "$OMARCHY_PATH/default/regions/cn/$source" "$target"
+  done
+  ;;
+*)
+  echo "Unknown region: $region" >&2
+  exit 1
+  ;;
+esac