feat(节点跟踪): 改进用户跟踪功能并添加新用户通知

当新用户首次发送消息时，返回布尔值并通知可用节点。在handler.py中添加对新用户的处理逻辑，当检测到新用户时，向其发送当前在线的节点列表。这有助于新用户更快了解可用资源。

bot/handler.py

@@ -132,7 +132,14 @@ async def _process_message(user_id: str, chat_id: str, text: str) -> None:
         from config import ROUTER_MODE
         if ROUTER_MODE:
             from router.nodes import get_node_registry
-            get_node_registry().track_user(user_id)
+            registry = get_node_registry()
+            is_new = registry.track_user(user_id)
+            if is_new:
+                nodes = registry.get_nodes_for_user(user_id)
+                online = [n for n in nodes if n.is_online]
+                if online:
+                    names = ", ".join(n.display_name for n in online)
+                    await send_text(chat_id, "chat_id", f"Available nodes: {names}")
 
         reply = await handle_command(user_id, text)
         if reply is not None:

router/nodes.py

@@ -69,9 +69,12 @@ class NodeRegistry:
             return True
         return secret == self._secret
 
-    def track_user(self, user_id: str) -> None:
-        """Record a user as known (has sent at least one message)."""
+    def track_user(self, user_id: str) -> bool:
+        """Record a user as known. Returns True if this is their first message."""
+        if user_id in self._known_users:
+            return False
         self._known_users.add(user_id)
+        return True
 
     def _get_notifiable_users(self, node: NodeConnection) -> Set[str]:
         """Get users to notify about a node event.