add dms-plugin-dev agent skill for plugin development (#2394)

.agents/skills/dms-plugin-dev/assets/templates/desktop/Settings.qml

@@ -0,0 +1,18 @@
+import QtQuick
+import qs.Common
+import qs.Widgets
+import qs.Modules.Plugins
+
+PluginSettings {
+    pluginId: "myDesktopWidget"
+
+    SliderSetting {
+        settingKey: "opacity"
+        label: "Opacity"
+        description: "Widget background opacity"
+        defaultValue: 85
+        minimum: 10
+        maximum: 100
+        unit: "%"
+    }
+}