feat: add draggable graph zones

tests/test_graph_explorer.py

@@ -428,6 +428,14 @@ def test_registry_serves_graph_explorer_exports(tmp_path: Path) -> None:
         assert "zoneDefinitionSets" in page
         assert "fabric-default" in page
         assert "collapsedZoneSnapshots" in page
+        assert "zoneDragState" in page
+        assert "startZoneDrag" in page
+        assert "moveZoneDrag" in page
+        assert "finishZoneDrag" in page
+        assert "Moved zone" in page
+        assert "cursor: grab" in page
+        assert "background: transparent" in page
+        assert "box-shadow: none" in page
         assert "collapseZone" in page
         assert "expandZone" in page
         assert "zoneCollapseNodeId" in page