7ea1fc2d69
Make Node Groups mutable instead of fixed-at-creation: - removeFromGroup / addToGroup store actions (inverse pair, history-aware) - right panel: per-member remove button + editable group description (reuses data.notes, no backend/serializer change) - drag a node over a group → confirm modal to add it (getIntersectingNodes) Tests: +21 (store, panel, canvas detection, modal). ha-relevant: yes