refactor(workflow): simplify edge configuration

backend/services/workflow_engine.py

@@ -113,14 +113,6 @@ class WorkflowEngine:
             return f"当满足以下条件时转到「{target}」：{condition}"
         return f"当当前阶段任务完成时转到「{target}」。"
 
-    def edge_transition_speech(self, edge: dict | None) -> str:
-        if not edge:
-            return ""
-        data = edge.get("data") or {}
-        return str(
-            data.get("transitionSpeech") or data.get("transition_speech") or ""
-        )
-
     def global_prompt(self) -> str:
         return str(self.settings.get("globalPrompt") or "").strip()