修复: rclone 后端列表不显示 + 调度审计 + 批量删除

1. 修复前端 rclone 后端 API 路径双重 /api 前缀导致 404，
   存储类型下拉框现在正确显示全部 70+ rclone 后端
2. 调度器自动触发的备份任务计入审计日志（用户名: system）
3. 新增备份记录批量删除 API (POST /api/backup/records/batch-delete)

server/internal/scheduler/service.go

@@ -17,12 +17,18 @@ type TaskRunner interface {
 	RunTaskByID(context.Context, uint) (*servicepkg.BackupRecordDetail, error)
 }
 
+// AuditRecorder 记录审计日志（可选依赖）
+type AuditRecorder interface {
+	Record(servicepkg.AuditEntry)
+}
+
 type Service struct {
 	mu      sync.Mutex
 	cron    *cron.Cron
 	tasks   repository.BackupTaskRepository
 	runner  TaskRunner
 	logger  *zap.Logger
+	audit   AuditRecorder
 	entries map[uint]cron.EntryID
 }
 
@@ -31,6 +37,8 @@ func NewService(tasks repository.BackupTaskRepository, runner TaskRunner, logger
 	return &Service{cron: cron.New(cron.WithParser(parser), cron.WithLocation(time.UTC)), tasks: tasks, runner: runner, logger: logger, entries: make(map[uint]cron.EntryID)}
 }
 
+func (s *Service) SetAuditRecorder(audit AuditRecorder) { s.audit = audit }
+
 func (s *Service) Start(ctx context.Context) error {
 	if err := s.Reload(ctx); err != nil {
 		return err
@@ -96,9 +104,19 @@ func (s *Service) syncTaskLocked(task *model.BackupTask) error {
 	if !task.Enabled || task.CronExpr == "" {
 		return nil
 	}
+	taskID := task.ID
+	taskName := task.Name
 	entryID, err := s.cron.AddFunc(task.CronExpr, func() {
-		if _, runErr := s.runner.RunTaskByID(context.Background(), task.ID); runErr != nil && s.logger != nil {
-			s.logger.Warn("scheduled backup run failed", zap.Uint("task_id", task.ID), zap.Error(runErr))
+		// 自动调度任务记录审计日志
+		if s.audit != nil {
+			s.audit.Record(servicepkg.AuditEntry{
+				Username: "system", Category: "backup_task", Action: "scheduled_run",
+				TargetType: "backup_task", TargetID: fmt.Sprintf("%d", taskID),
+				TargetName: taskName, Detail: fmt.Sprintf("定时调度触发备份任务: %s (cron: %s)", taskName, task.CronExpr),
+			})
+		}
+		if _, runErr := s.runner.RunTaskByID(context.Background(), taskID); runErr != nil && s.logger != nil {
+			s.logger.Warn("scheduled backup run failed", zap.Uint("task_id", taskID), zap.Error(runErr))
 		}
 	})
 	if err != nil {