feat: 多班级版 v2.0 - Go后端重写 + 43轮代码审查

- 后端从 Python FastAPI 重写为 Go Gin（端口 56789）
- 多班级完全隔离
- 超级管理员独立登录
- 课代表作业管理、排行榜分项排行
- 角色加减分上下限可配置
- 家长改密功能（可开关）
- 周度/月度重置功能
- MySQL 5.7 兼容
- 43轮代码审查+全部修复
- Apache 2.0 许可证

backend-go/internal/service/log_service.go

@@ -0,0 +1,70 @@
+// ===========================================
+// 多班级版班级管理系统 - Go 后端
+//
+// 开发者: Canglan
+// 联系方式: admin@sea-studio.top
+// 版权归属: Sea Network Technology Studio
+// 许可证: Apache License 2.0
+//
+// 版权所有 © Sea Network Technology Studio
+// ===========================================
+
+package service
+
+import (
+	"hz-gitea.sea-studio.top/canglan/SharedClassManager/internal/model"
+	"hz-gitea.sea-studio.top/canglan/SharedClassManager/internal/repository"
+	"hz-gitea.sea-studio.top/canglan/SharedClassManager/pkg/logger"
+)
+
+// LogService 日志服务
+type LogService struct {
+	logRepo *repository.LogRepo
+}
+
+// NewLogService 创建日志服务
+func NewLogService(logRepo *repository.LogRepo) *LogService {
+	return &LogService{logRepo: logRepo}
+}
+
+// WriteLoginLog 写入登录日志
+func (s *LogService) WriteLoginLog(username string, loginResult int8, ip, userAgent, failReason string) {
+	log := &model.LoginLog{
+		Username:    username,
+		LoginResult: loginResult,
+		IPAddress:   stringPtr(ip),
+		UserAgent:   stringPtr(userAgent),
+		FailReason:  stringPtr(failReason),
+	}
+	if _, err := s.logRepo.CreateLoginLog(log); err != nil {
+		logger.Sugared.Errorf("写入登录日志失败: %v", err)
+	}
+}
+
+// WriteOperationLog 写入操作日志
+func (s *LogService) WriteOperationLog(operatorID int, operatorName, operatorRole, operationType string,
+	targetType *string, targetID *int, details *string, ip *string, classID *int) {
+	log := &model.OperationLog{
+		OperatorID:    operatorID,
+		OperatorName:  stringPtr(operatorName),
+		OperatorRole:  stringPtr(operatorRole),
+		OperationType: operationType,
+		TargetType:    targetType,
+		TargetID:      targetID,
+		Details:       details,
+		IPAddress:     ip,
+		ClassID:       classID,
+	}
+	if _, err := s.logRepo.CreateOperationLog(log); err != nil {
+		logger.Sugared.Errorf("写入操作日志失败: %v", err)
+	}
+}
+
+// stringPtr 辅助函数：字符串转指针（空字符串返回 nil）
+func stringPtr(s string) *string {
+	if s == "" {
+		return nil
+	}
+	return &s
+}
+