Consolidate layers into groups

`Konva warning: The stage has 20 layers. Recommended maximin number of layers is 3-5. Adding more layers into the stage may drop the performance. Rethink your tree structure, you can use Konva.Group.`

Locate where the Konva stage and its layers are constructed, then inspect how the scene tree is organized. Consolidate the layers into Konva.Group structures as appropriate; done means the stage no longer has the problematic layer count and the warning is resolved without losing the existing scene behavior.

Written by the indexing model from the issue text.