feat: Agent 服务日志功能和后端更新

- agent/main.py: 添加日志记录功能
- agent/llm: 更新 anthropic, openai, factory
- agent/core/agent.py: 更新
- server: agent_handler, agent_service, chat_service 更新

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/model/agent.go

@@ -105,6 +105,7 @@ type AgentRequest struct {
 	AgentID   string                 `json:"agent_id" binding:"required"`
 	Message   string                 `json:"message" binding:"required"`
 	SessionID string                 `json:"session_id"`
+	ModelID   string                 `json:"model_id"`
 	Context   map[string]interface{} `json:"context"`
 }