feat: 实现 AI-First 代理系统

核心功能:
- AIAgent 模型：AI 代理身份管理
- AIOperationLog: AI 操作日志记录
- AITask: AI 异步任务系统
- AIWebhook: AI webhook 订阅

API 端点:
- POST /api/agents/auth/ - AI 代理认证
- GET/POST /api/agents/ - 代理管理
- GET /api/agent-logs/ - 操作日志查询
- GET/POST /api/agent-tasks/ - 任务管理
- GET/POST /api/agent-webhooks/ - Webhook 管理
- POST /api/batch/ - 批量操作

预置 AI 代理:
- content-moderator-ai: 内容审核 AI
- content-generator-ai: 内容生成 AI
- service-curator-ai: 服务推荐 AI
- analytics-ai: 数据分析 AI
- admin-ai: 管理员 AI

文档:
- AI_AGENT.md: AI-First 设计文档
- init_agents.py: AI 代理初始化脚本

测试:
- 认证系统测试通过
- JWT token 生成正常
- 权限系统工作正常

city-manual/backend/agents/serializers.py

@@ -0,0 +1,131 @@
+from rest_framework import serializers
+from .models import AIAgent, AIOperationLog, AITask, AIWebhook
+
+
+class AIAgentSerializer(serializers.ModelSerializer):
+    """AI 代理序列化器"""
+    
+    permissions = serializers.ListField(
+        child=serializers.CharField(),
+        required=False
+    )
+    
+    class Meta:
+        model = AIAgent
+        fields = [
+            'id', 'agent_id', 'name', 'description', 'permissions',
+            'rate_limit', 'rate_limit_window', 'is_active', 'last_seen',
+            'created_at', 'updated_at'
+        ]
+        read_only_fields = ['id', 'created_at', 'updated_at', 'last_seen']
+        extra_kwargs = {
+            'secret_key': {'write_only': True}
+        }
+
+
+class AIAgentAuthSerializer(serializers.Serializer):
+    """AI 代理认证序列化器"""
+    
+    agent_id = serializers.CharField()
+    agent_secret = serializers.CharField()
+    
+    def validate(self, data):
+        try:
+            agent = AIAgent.objects.get(
+                agent_id=data['agent_id'],
+                secret_key=data['agent_secret'],
+                is_active=True
+            )
+        except AIAgent.DoesNotExist:
+            raise serializers.ValidationError("Invalid agent credentials")
+        
+        # 更新最后活跃时间
+        from django.utils import timezone
+        agent.last_seen = timezone.now()
+        agent.save()
+        
+        self.instance = agent
+        return data
+
+
+class AIOperationLogSerializer(serializers.ModelSerializer):
+    """AI 操作日志序列化器"""
+    
+    agent_id = serializers.CharField(source='agent.agent_id', read_only=True)
+    agent_name = serializers.CharField(source='agent.name', read_only=True)
+    
+    class Meta:
+        model = AIOperationLog
+        fields = [
+            'id', 'agent_id', 'agent_name', 'action', 'resource_type',
+            'resource_id', 'status', 'confidence', 'reasoning',
+            'execution_time_ms', 'created_at'
+        ]
+        read_only_fields = ['id', 'created_at']
+
+
+class AITaskSerializer(serializers.ModelSerializer):
+    """AI 任务序列化器"""
+    
+    agent_id = serializers.CharField(source='agent.agent_id', read_only=True)
+    
+    class Meta:
+        model = AITask
+        fields = [
+            'id', 'task_id', 'agent_id', 'task_type', 'status',
+            'progress', 'processed_items', 'total_items', 'result',
+            'error_message', 'callback_url', 'created_at', 'started_at', 'completed_at'
+        ]
+        read_only_fields = ['id', 'created_at', 'started_at', 'completed_at']
+
+
+class AITaskCreateSerializer(serializers.Serializer):
+    """AI 任务创建序列化器"""
+    
+    task_type = serializers.CharField()
+    operations = serializers.ListField(required=False)
+    callback_url = serializers.URLField(required=False)
+    
+    def validate(self, data):
+        if data['task_type'] == 'batch' and not data.get('operations'):
+            raise serializers.ValidationError("Batch task requires operations")
+        return data
+
+
+class AIWebhookSerializer(serializers.ModelSerializer):
+    """AI Webhook 序列化器"""
+    
+    agent_id = serializers.CharField(source='agent.agent_id', read_only=True)
+    
+    class Meta:
+        model = AIWebhook
+        fields = [
+            'id', 'agent_id', 'event', 'url', 'is_active',
+            'last_triggered', 'failure_count', 'created_at'
+        ]
+        read_only_fields = ['id', 'created_at', 'last_triggered', 'failure_count']
+        extra_kwargs = {
+            'secret': {'write_only': True}
+        }
+
+
+class BatchOperationSerializer(serializers.Serializer):
+    """批量操作序列化器"""
+    
+    operations = serializers.ListField(
+        child=serializers.DictField()
+    )
+    
+    def validate_operations(self, operations):
+        if len(operations) > 100:
+            raise serializers.ValidationError("Maximum 100 operations per batch")
+        
+        for i, op in enumerate(operations):
+            if 'method' not in op:
+                raise serializers.ValidationError(f"Operation {i}: missing 'method'")
+            if op['method'] not in ['GET', 'POST', 'PUT', 'PATCH', 'DELETE']:
+                raise serializers.ValidationError(f"Operation {i}: invalid method")
+            if 'path' not in op:
+                raise serializers.ValidationError(f"Operation {i}: missing 'path'")
+        
+        return operations