Merge omacom/omarchy-iso#236 regional ISO builds, as an install-time choice

Every ISO bundles the cn profile; the first-screen pick decides. --region cn
only preselects China and names the artifact. The region value is cn, the cn
timezone is preselected when China is chosen, and the profile packages and
ArchLinuxCN keyring reach the target only for China.

test/unit/test_pin_local_packages.py

@@ -104,7 +104,7 @@ class RuntimePackagesTest(unittest.TestCase):
                  mock.patch.object(phases_impl, "_early_packages", return_value=["git"]), \
                  mock.patch.object(phases_impl, "_package_targets", return_value={
                      "runtime": "omarchy-dev", "settings": "omarchy-settings-dev", "nvim": "omarchy-nvim"}):
-                return phases_impl._runtime_package_list(types.SimpleNamespace())
+                return phases_impl._runtime_package_list(types.SimpleNamespace(omarchy_install={"region": "global"}))
 
     def test_local_builds_install_on_every_region(self):
         packages = self.runtime_packages("omarchy-dev\nomarchy-settings-dev\nrime-ice-installer\n")