fix: 迭代计数修复 — stateChange 也携带迭代号，双通道同步

- IPC handler 将 stateChange 事件转发到渲染进程
- useAgentStream 同时监听 streamEvent 和 stateChange 更新迭代
- 切换会话/发消息时重置 currentIteration 为 0
- 添加 console.log 诊断日志

electron/ipc/handlers.ts

@@ -84,9 +84,13 @@ export function registerAllIPCHandlers(
       }
     };
 
-    const onStateChange = (data: { previous: string; current: string }) => {
+    const onStateChange = (data: { previous?: string; current?: string; sessionId?: string; iteration?: number; state?: string }) => {
       // AGENT 层：记录状态转换
-      log.info(`[AGENT] State: ${data.previous} → ${data.current}`);
+      if (data.previous) log.info(`[AGENT] State: ${data.previous} → ${data.current}`);
+      // 转发到渲染进程（携带迭代号）
+      if (!mainWindow.isDestroyed()) {
+        mainWindow.webContents.send('agent:stateChange', data);
+      }
     };
 
     agentLoop.on('streamEvent', onStreamEvent);