fix: improve node group management in graph editor

[otto-link]

Improve group management in the graph editor.

Currently, once nodes have been added to a group, there is no way to ungroup them as a group. Users have to move the nodes out of the group one by one.

Add proper group management operations, including:

• Ungroup a group while keeping all its nodes.
• Preserve the nodes' positions and connections when ungrouping.
• Allow the operation to be applied to the entire group at once.
• Ensure grouping and ungrouping remain intuitive and consistent with the existing graph editor interactions.