Enhance workflow engine and frontend components with transition speech support

- Introduce edge transition speech functionality in the WorkflowEngine to provide optional speech during node transitions.
- Update pipeline execution to utilize the new transition speech feature, enhancing user experience by masking delays during transitions.
- Modify frontend components to support transition speech in edge specifications, allowing users to define and edit transition speech for edges.
- Refactor edge handling logic in the WorkflowEditor to accommodate the new transition speech field, improving workflow management capabilities.

backend/services/workflow_engine.py

@@ -50,6 +50,18 @@ class WorkflowEngine:
     def edge_condition(self, edge: dict) -> str:
         return (edge.get("data") or {}).get("condition") or ""
 
+    def edge_transition_speech(self, edge: dict | None) -> str:
+        """命中该边、切换节点瞬间播报的过渡语(可选,掩盖延迟,不写入上下文)。"""
+        if not edge:
+            return ""
+        return (edge.get("data") or {}).get("transition_speech") or ""
+
+    def find_edge(self, source: str | None, target: str | None) -> dict | None:
+        for edge in self.edges:
+            if edge.get("source") == source and edge.get("target") == target:
+                return edge
+        return None
+
     def edge_description(self, edge: dict) -> str:
         """作为转移函数的 description 交给 LLM:满足该条件时模型应调用此函数。"""
         cond = self.edge_condition(edge)