For local gadgets, their source and resources should be located in the same folder.
See the example about the To-do gadget:
Note
The Gadget importer service will find a folder that contains the gadget source, then find all resources in the folder and store them into JCR as the resources of the gadget. Therefore, putting the gadget resources in the folder different from the gadget source can cause many unnecessary files to be stored as the resource files of the gadget.