feat: 添加左侧面板选项卡状态管理，更新流程节点数据结构

ccw/frontend/src/stores/flowStore.ts

@@ -44,6 +44,7 @@ const initialState = {
   // UI state
   isPaletteOpen: true,
   isPropertyPanelOpen: true,
+  leftPanelTab: 'nodes' as const,
 };
 
 export const useFlowStore = create<FlowStore>()(
@@ -429,6 +430,10 @@ export const useFlowStore = create<FlowStore>()(
         set({ isPropertyPanelOpen: open }, false, 'setIsPropertyPanelOpen');
       },
 
+      setLeftPanelTab: (tab) => {
+        set({ leftPanelTab: tab }, false, 'setLeftPanelTab');
+      },
+
       // ========== Utility ==========
 
       resetFlow: () => {