fix: set default imageObject to Atlas_Core.Content.Mendix in Image template

When the Image widget datasource mode is "image" (the default), Studio
Pro requires an image to be selected — otherwise it shows "No image
selected." Set the template default to the Mendix logo image from
Atlas_Core, matching what Studio Pro sets when creating a new Image
widget.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

sdk/widgets/templates/mendix-11.6/image.json

@@ -60,7 +60,7 @@
           "Expression": "",
           "Form": "",
           "Icon": null,
-          "Image": "",
+          "Image": "Atlas_Core.Content.Mendix",
           "Microflow": "",
           "Nanoflow": "",
           "Objects": [