🔔 飞行侠实现：实例注册 + Webhook 推送

新功能:
- instances 应用：OpenClaw 实例管理
- Instance 模型：实例注册，Agent 列表，Webhook URL
- MeetingInstanceMap：会议 - 实例映射
- Webhook 推送：消息发送时自动通知相关实例

API 端点:
- POST /api/v1/instances/register/ - 实例注册
- POST /api/v1/instances/join-meeting/ - 加入会议
- GET  /api/v1/instances/ - 实例列表
- POST /api/v1/instances/webhook-test/ - Webhook 测试

集成:
- send_message API 自动触发 Webhook 推送
- 支持广播和定向推送

测试:
- test_webhook.py: 完整测试流程

使用场景:
1. 每台 OpenClaw 机器注册实例
2. Agent 加入会议时关联实例
3. 消息发送时推送到对应机器
4. 本机 OpenClaw 收到通知，触发 Agent 响应

backend/instances/views.py

@@ -0,0 +1,118 @@
+from rest_framework import serializers, status, views
+from rest_framework.response import Response
+from rest_framework.decorators import api_view
+from .models import Instance, MeetingInstanceMap
+from .webhook import register_instance, join_meeting
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class InstanceRegisterSerializer(serializers.Serializer):
+    instance_id = serializers.CharField(max_length=100)
+    instance_name = serializers.CharField(max_length=200)
+    agent_ids = serializers.ListField(child=serializers.CharField())
+    webhook_url = serializers.URLField()
+
+
+class InstanceRegisterView(views.APIView):
+    """
+    实例注册接口
+    
+    POST /api/v1/instances/register/
+    {
+        "instance_id": "phospher-openclaw",
+        "instance_name": "飞行侠的 OpenClaw",
+        "agent_ids": ["flying_hero", "lobster_monitor"],
+        "webhook_url": "http://192.168.1.100:8888/meeting-notify"
+    }
+    """
+    def post(self, request):
+        serializer = InstanceRegisterSerializer(data=request.data)
+        if not serializer.is_valid():
+            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+        
+        try:
+            instance = register_instance(
+                instance_id=serializer.validated_data['instance_id'],
+                instance_name=serializer.validated_data['instance_name'],
+                agent_ids=serializer.validated_data['agent_ids'],
+                webhook_url=serializer.validated_data['webhook_url']
+            )
+            
+            return Response({
+                'status': 'success',
+                'instance_id': str(instance.id),
+                'message': f'实例 {instance.instance_name} 注册成功'
+            })
+        except Exception as e:
+            logger.error(f"注册失败：{e}")
+            return Response({'error': str(e)}, status=status.HTTP_500_INTERNAL_SERVER_ERROR)
+
+
+class MeetingJoinSerializer(serializers.Serializer):
+    instance_id = serializers.CharField(max_length=100)
+    meeting_id = serializers.UUIDField()
+    agent_ids = serializers.ListField(child=serializers.CharField())
+
+
+class MeetingJoinView(views.APIView):
+    """
+    实例加入会议
+    
+    POST /api/v1/instances/join-meeting/
+    {
+        "instance_id": "phospher-openclaw",
+        "meeting_id": "xxx-xxx-xxx",
+        "agent_ids": ["flying_hero"]
+    }
+    """
+    def post(self, request):
+        serializer = MeetingJoinSerializer(data=request.data)
+        if not serializer.is_valid():
+            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+        
+        try:
+            join_meeting(
+                instance_id=serializer.validated_data['instance_id'],
+                meeting_id=serializer.validated_data['meeting_id'],
+                agent_ids=serializer.validated_data['agent_ids']
+            )
+            
+            return Response({'status': 'success', 'message': '已加入会议'})
+        except Instance.DoesNotExist:
+            return Response({'error': '实例不存在'}, status=status.HTTP_404_NOT_FOUND)
+        except Exception as e:
+            logger.error(f"加入会议失败：{e}")
+            return Response({'error': str(e)}, status=status.HTTP_500_INTERNAL_SERVER_ERROR)
+
+
+class InstanceListView(views.APIView):
+    """
+    获取实例列表
+    
+    GET /api/v1/instances/
+    """
+    def get(self, request):
+        instances = Instance.objects.filter(is_active=True)
+        data = [{
+            'id': str(i.id),
+            'instance_id': i.instance_id,
+            'instance_name': i.instance_name,
+            'agent_ids': i.agent_ids,
+            'webhook_url': i.webhook_url,
+            'last_heartbeat': i.last_heartbeat.isoformat() if i.last_heartbeat else None
+        } for i in instances]
+        
+        return Response(data)
+
+
+class WebhookNotifyView(views.APIView):
+    """
+    Webhook 通知接收（测试用）
+    
+    POST /api/v1/instances/webhook-test/
+    """
+    def post(self, request):
+        logger.info(f"📬 收到 Webhook 通知：{request.data}")
+        return Response({'status': 'received'})