Rename OEM vocabulary to provisioning (ISO)

Matches the runtime rename. The deferred-provisioning install mode replaces
'OEM' everywhere:
  omarchy_install.oem            → omarchy_install.defer_provisioning
  --oem / --oem-file             → --defer-provisioning / --defer-provisioning-file
  OMARCHY_INSTALL_OEM_FILE       → OMARCHY_INSTALL_DEFER_PROVISIONING_FILE
  cidata 'oem' marker            → 'defer-provisioning'
  /var/lib/omarchy/oem/          → /var/lib/omarchy/provisioning/
  /etc/omarchy/oem.key           → /etc/omarchy/provisioning.key
  install/oem/omarchy-oem-setup.service → install/provisioning/omarchy-provision-owner.service
  stage_oem_state phase          → stage_provisioning_state ('Staging provisioning')

Orchestrator internals (OEM_STATE_DIR, _validate_oem_state, ctx.oem, …),
the configurator, cidata-load, the dashboard phase band, the harness
(--oem → --provision), and the tests all move together.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/test_configure_ssh_access.py

@@ -60,7 +60,7 @@ class ConfigureSshAccessTest(unittest.TestCase):
         if authorized_keys is not None:
             authorized_keys_path = self.target / "authorized_keys"
             authorized_keys_path.write_text(authorized_keys)
-        return types.SimpleNamespace(target=self.target, username="jeff", authorized_keys_path=authorized_keys_path, oem=False)
+        return types.SimpleNamespace(target=self.target, username="jeff", authorized_keys_path=authorized_keys_path, defer_provisioning=False)
 
     def configure(self, **kwargs):
         phases_impl.configure_ssh_access(self.ctx(**kwargs))