PutGlobalSettingTool
settings put global <key> <value> — write a Settings.Global value (e.g. airplane_mode_on, wifi_on). Idempotent. Delegates to putSetting; treated as failure on non-zero exit or non-empty stderr.
Privilege: requires a working ShellBackend.
Params: key (required), value (required).
On success the result map carries success (true), namespace ("global"), key, and value.