settings: enforce administrator-managed lock settings (#3897)

port 2.0

(cherry picked from commit 404c9672d7)

quickshell/DMSShellIPC.qml

@@ -1104,6 +1104,8 @@ Item {
         function set(key: string, value: string): string {
             if (AdminPolicy.disableSettingsIpcSet)
                 return "SETTINGS_SET_DISABLED";
+            if (SettingsData.isManaged(key))
+                return "SETTINGS_SET_MANAGED";
             if (!(key in SettingsData)) {
                 log.warn("Cannot set property, not found:", key);
                 return "SETTINGS_INVALID_KEY";