refactor: move workflow package to dify_graph (#32844)

api/dify_graph/graph_engine/domain/__init__.py

@@ -0,0 +1,14 @@
+"""
+Domain models for graph engine.
+
+This package contains the core domain entities, value objects, and aggregates
+that represent the business concepts of workflow graph execution.
+"""
+
+from .graph_execution import GraphExecution
+from .node_execution import NodeExecution
+
+__all__ = [
+    "GraphExecution",
+    "NodeExecution",
+]