Restrict third-party shell plugin capabilities

Reported-by: Roger Piñol <rogerpicar@gmail.com>

shell/services/PluginRegistryApi.qml

@@ -0,0 +1,32 @@
+import QtQuick
+
+// Read-only, self-scoped registry view for an installed third-party plugin.
+// The host updates manifest/enabled when it rescans; no host registry object is
+// retained here, so `parent` and property traversal cannot reach ShellRoot.
+QtObject {
+  id: api
+
+  required property string pluginId
+  property var manifest: null
+  property bool enabled: false
+  property var _entryPointUrl: null
+
+  readonly property var installedPlugins: {
+    var out = ({})
+    if (manifest) out[pluginId] = manifest
+    return out
+  }
+
+  function isEnabled(id) {
+    return String(id || "") === pluginId && enabled
+  }
+
+  function resolveEnabledId(id) {
+    return String(id || "") === pluginId ? pluginId : ""
+  }
+
+  function entryPointUrl(candidate, kind) {
+    if (!candidate || String(candidate.id || "") !== pluginId) return ""
+    return _entryPointUrl ? _entryPointUrl(String(kind || "")) : ""
+  }
+}