feat: 更新后端服务

- agent_handler.go: 新增agent管理接口
- agent_service.go: 扩展agent服务逻辑
- skill_handler.go: 更新skill接口
- chat_service.go: 更新chat服务
- model相关: 新增model仓库和服务
- main.go: 更新路由配置

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

server/internal/service/chat_service.go

@@ -166,14 +166,11 @@ func (s *ChatService) ListAgents(userID string) ([]model.Agent, error) {
 // CreateAgent 创建新的 Agent
 func (s *ChatService) CreateAgent(userID string, name, description string) (*model.Agent, error) {
 	agent := &model.Agent{
-		ID:           uuid.New().String(),
-		Name:         name,
-		Description:  description,
-		OwnerID:      userID,
-		SecurityLevel: model.SecurityLevelSafe,
-		IsActive:     true,
-		Timeout:      60,
-		MemoryLimit:  134217728, // 128MB
+		ID:          uuid.New().String(),
+		Name:        name,
+		Description: description,
+		OwnerID:     userID,
+		IsActive:    true,
 	}
 
 	if err := s.agentRepo.Create(agent); err != nil {