feat(backup): 新增 zstd 压缩选项 (#89)

备份压缩在 gzip 之外新增 zstd（更高压缩率、更快解压）。pkg/compress 新增 ZstdFile/UnzstdFile，Master 与 Agent 压缩/解压按后缀分流，任务校验与前端下拉同步；往返单测覆盖。

server/internal/service/backup_execution_service.go

@@ -726,6 +726,15 @@ func (s *BackupExecutionService) executeTask(ctx context.Context, task *model.Ba
 			return
 		}
 		finalPath = compressedPath
+	} else if strings.EqualFold(task.Compression, "zstd") && !strings.HasSuffix(strings.ToLower(finalPath), ".zst") {
+		logger.Infof("开始压缩备份文件（zstd）")
+		compressedPath, compressErr := compress.ZstdFile(finalPath)
+		if compressErr != nil {
+			errMessage = compressErr.Error()
+			logger.Errorf("压缩备份文件失败：%v", compressErr)
+			return
+		}
+		finalPath = compressedPath
 	}
 	if task.Encrypt {
 		logger.Infof("开始加密备份文件")

server/internal/service/backup_task_service.go

@@ -40,7 +40,7 @@ type BackupTaskUpsertInput struct {
 	NodePoolTag   string `json:"nodePoolTag" binding:"max=64"`
 	Tags          string `json:"tags" binding:"max=500"` // 逗号分隔标签
 	RetentionDays int    `json:"retentionDays"`
-	Compression   string `json:"compression" binding:"omitempty,oneof=gzip none"`
+	Compression   string `json:"compression" binding:"omitempty,oneof=gzip zstd none"`
 	Encrypt       bool   `json:"encrypt"`
 	MaxBackups    int    `json:"maxBackups"`
 	// ExtraConfig 类型特有扩展配置（如 SAP HANA 的 backupLevel/backupChannels）

server/internal/service/execution_helpers.go

@@ -106,6 +106,16 @@ func prepareBackupArtifact(cipher *codec.ConfigCipher, artifactPath string, logg
 		}
 		current = decompressed
 	}
+	if strings.HasSuffix(strings.ToLower(current), ".zst") {
+		if logger != nil {
+			logger.Infof("检测到 zstd 压缩，开始解压")
+		}
+		decompressed, err := compress.UnzstdFile(current)
+		if err != nil {
+			return "", err
+		}
+		current = decompressed
+	}
 	return current, nil
 }