Chore: use `Workflow.VERSION_DRAFT` instead of hardcoded `draft` (#23136)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/core/tools/workflow_as_tool/tool.py

         if not version:
             workflow = (
                 db.session.query(Workflow)
-                .where(Workflow.app_id == app_id, Workflow.version != "draft")
+                .where(Workflow.app_id == app_id, Workflow.version != Workflow.VERSION_DRAFT)
                 .order_by(Workflow.created_at.desc())
                 .first()
             )

api/services/workflow/workflow_converter.py

             tenant_id=app_model.tenant_id,
             app_id=app_model.id,
             type=WorkflowType.from_app_mode(new_app_mode).value,
-            version="draft",
+            version=Workflow.VERSION_DRAFT,
             graph=json.dumps(graph),
             features=json.dumps(features),
             created_by=account_id,

api/services/workflow_service.py

         workflow = (
             db.session.query(Workflow)
             .where(
-                Workflow.tenant_id == app_model.tenant_id, Workflow.app_id == app_model.id, Workflow.version == "draft"
+                Workflow.tenant_id == app_model.tenant_id,
+                Workflow.app_id == app_model.id,
+                Workflow.version == Workflow.VERSION_DRAFT,
             )
             .first()
         )
                 tenant_id=app_model.tenant_id,
                 app_id=app_model.id,
                 type=WorkflowType.from_app_mode(app_model.mode).value,
-                version="draft",
+                version=Workflow.VERSION_DRAFT,
                 graph=json.dumps(graph),
                 features=json.dumps(features),
                 created_by=account.id,
         draft_workflow_stmt = select(Workflow).where(
             Workflow.tenant_id == app_model.tenant_id,
             Workflow.app_id == app_model.id,
-            Workflow.version == "draft",
+            Workflow.version == Workflow.VERSION_DRAFT,
         )
         draft_workflow = session.scalar(draft_workflow_stmt)
         if not draft_workflow:
             tenant_id=app_model.tenant_id,
         )
 
-        eclosing_node_type_and_id = draft_workflow.get_enclosing_node_type_and_id(node_config)
-        if eclosing_node_type_and_id:
-            _, enclosing_node_id = eclosing_node_type_and_id
+        enclosing_node_type_and_id = draft_workflow.get_enclosing_node_type_and_id(node_config)
+        if enclosing_node_type_and_id:
+            _, enclosing_node_id = enclosing_node_type_and_id
         else:
             enclosing_node_id = None
 
             raise ValueError(f"Workflow with ID {workflow_id} not found")
 
         # Check if workflow is a draft version
-        if workflow.version == "draft":
+        if workflow.version == Workflow.VERSION_DRAFT:
             raise DraftWorkflowDeletionError("Cannot delete draft workflow versions")
 
         # Check if this workflow is currently referenced by an app