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.

frontend/src/components/workflow/specs.ts

@@ -99,7 +99,7 @@ export type WorkflowGraph = {
     id: string;
     source: string;
     target: string;
-    data?: { condition?: string; label?: string };
+    data?: { condition?: string; label?: string; transition_speech?: string };
   }>;
   viewport?: { x: number; y: number; zoom: number };
 };