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.

backend/services/config_resolver.py

@@ -66,6 +66,8 @@ async def resolve_runtime_config(
         prompt=assistant.prompt or "你是一个有帮助的助手。",
         runtimeMode=assistant.runtime_mode,  # type: ignore[arg-type]
         enableInterrupt=assistant.enable_interrupt,
+        # workflow 图:仅 workflow 类型非空,引擎据此启用图驱动对话
+        graph=(assistant.graph or {}) if assistant.type == "workflow" else {},
         # 模型/音色:模型资源中的配置优先
         model=str(_value(llm_resource, "modelId", "")),
         asr=str(_value(stt_resource, "modelId", "")),