feat: include is_flow_synced and source_tree_name in step list/detail responses

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/steps.py

@@ -247,6 +247,8 @@ async def get_step(
         "is_active": step.is_active,
         "created_at": step.created_at,
         "updated_at": step.updated_at,
+        "is_flow_synced": step.is_flow_synced,
+        "source_tree_name": step.source_tree.name if step.source_tree else None,
     }
 
     # Get category name if exists