feat: 实现多主机架构的核心组件

新增路由器、主机客户端和共享协议模块，支持多主机部署模式：
- 路由器作为中央节点管理主机连接和消息路由
- 主机客户端作为工作节点运行本地代理
- 共享协议定义通信消息格式
- 新增独立运行模式standalone.py
- 更新配置系统支持路由模式

agent/task_runner.py

@@ -30,6 +30,7 @@ class BackgroundTask:
     result: Optional[str] = None
     error: Optional[str] = None
     notify_chat_id: Optional[str] = None
+    user_id: Optional[str] = None
 
     @property
     def elapsed(self) -> float:
@@ -44,12 +45,18 @@ class TaskRunner:
     def __init__(self) -> None:
         self._tasks: Dict[str, BackgroundTask] = {}
         self._lock = asyncio.Lock()
+        self._notification_handler: Optional[Callable] = None
+
+    def set_notification_handler(self, handler: Optional[Callable]) -> None:
+        """Set custom notification handler for M3 mode (host client -> router)."""
+        self._notification_handler = handler
 
     async def submit(
         self,
         coro: Callable[[], Any],
         description: str,
         notify_chat_id: Optional[str] = None,
+        user_id: Optional[str] = None,
     ) -> str:
         """Submit a coroutine as a background task."""
         task_id = str(uuid.uuid4())[:8]
@@ -59,6 +66,7 @@ class TaskRunner:
             started_at=time.time(),
             status=TaskStatus.PENDING,
             notify_chat_id=notify_chat_id,
+            user_id=user_id,
         )
 
         async with self._lock:
@@ -94,7 +102,10 @@ class TaskRunner:
             logger.exception("Task %s failed: %s", task_id, exc)
 
         if task.notify_chat_id:
-            await self._send_notification(task)
+            if self._notification_handler:
+                await self._notification_handler(task)
+            else:
+                await self._send_notification(task)
 
     async def _send_notification(self, task: BackgroundTask) -> None:
         """Send Feishu notification about task completion."""