Enhance workflow engine and integration in backend and frontend

- Introduce a new WorkflowEngine class to manage workflow graphs, enabling dynamic node-based interactions.
- Update AssistantConfig to include a graph field for workflow definitions, allowing for flexible configuration.
- Modify pipeline execution to support workflow-driven dialogue, integrating node transitions and system prompts based on active nodes.
- Enhance frontend components to visualize active nodes and provide debugging capabilities, including highlighting the current node during interactions.
- Refactor existing components to accommodate new workflow functionalities and improve overall user experience.

frontend/src/components/workflow/WorkflowEditor.tsx

@@ -50,6 +50,7 @@ import { Textarea } from "@/components/ui/textarea";
 
 import { edgeTypes } from "./ConditionEdge";
 import {
+  ActiveNodeContext,
   EdgeActionContext,
   NodeActionContext,
   NodeSpecsContext,
@@ -81,6 +82,8 @@ export type WorkflowEditorProps = {
   settings: WorkflowSettings;
   onSettingsChange: (settings: WorkflowSettings) => void;
   modelOptions: { llm: ModelOption[]; asr: ModelOption[]; tts: ModelOption[] };
+  /** 调试通话中当前激活的节点 id(用于高亮)。 */
+  activeNodeId?: string | null;
 };
 
 let nodeSeq = 0;
@@ -127,6 +130,7 @@ function Canvas({
   settings,
   onSettingsChange,
   modelOptions,
+  activeNodeId,
   specsByType,
 }: WorkflowEditorProps & { specsByType: NodeSpecMap }) {
   const initial = useMemo(() => toFlow(value ?? defaultGraph()), [value]);
@@ -252,6 +256,7 @@ function Canvas({
 
   return (
     <NodeSpecsContext.Provider value={specsByType}>
+      <ActiveNodeContext.Provider value={activeNodeId ?? null}>
       <NodeActionContext.Provider value={nodeActions}>
         <EdgeActionContext.Provider value={edgeActions}>
           <div className="h-full w-full overflow-hidden rounded-2xl border border-hairline bg-canvas-soft">
@@ -446,6 +451,7 @@ function Canvas({
           </div>
         </EdgeActionContext.Provider>
       </NodeActionContext.Provider>
+      </ActiveNodeContext.Provider>
     </NodeSpecsContext.Provider>
   );
 }