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/http/backup_record_handler.go

@@ -147,6 +147,24 @@ func (h *BackupRecordHandler) Delete(c *gin.Context) {
 	response.Success(c, gin.H{"deleted": true})
 }
 
+func (h *BackupRecordHandler) BatchDelete(c *gin.Context) {
+	var input struct {
+		IDs []uint `json:"ids" binding:"required,min=1"`
+	}
+	if err := c.ShouldBindJSON(&input); err != nil {
+		response.Error(c, apperror.BadRequest("BACKUP_RECORD_BATCH_INVALID", "批量删除参数不合法", err))
+		return
+	}
+	deleted := 0
+	for _, id := range input.IDs {
+		if err := h.service.Delete(c.Request.Context(), id); err == nil {
+			deleted++
+		}
+	}
+	recordAudit(c, h.auditService, "backup_record", "batch_delete", "backup_record", "", "", fmt.Sprintf("批量删除 %d 条备份记录", deleted))
+	response.Success(c, gin.H{"deleted": deleted})
+}
+
 func buildRecordFilter(c *gin.Context) (service.BackupRecordListInput, error) {
 	var filter service.BackupRecordListInput
 	if taskIDValue := strings.TrimSpace(c.Query("taskId")); taskIDValue != "" {

server/internal/http/router.go

@@ -106,6 +106,7 @@ func NewRouter(deps RouterDependencies) *gin.Engine {
 		backupRecords.GET("/:id/logs/stream", backupRecordHandler.StreamLogs)
 		backupRecords.GET("/:id/download", backupRecordHandler.Download)
 		backupRecords.POST("/:id/restore", backupRecordHandler.Restore)
+		backupRecords.POST("/batch-delete", backupRecordHandler.BatchDelete)
 		backupRecords.DELETE("/:id", backupRecordHandler.Delete)
 		dashboard := api.Group("/dashboard")
 		dashboard.Use(AuthMiddleware(deps.JWTManager))