fix(hostupdate): Windows 编译兼容 - 磁盘空间预检拆分为平台实现 (#363)

Co-authored-by: libiao320-cmd <280725528+libiao320-cmd@users.noreply.github.com>

backend/internal/hostupdate/manager_ops.go

@@ -17,7 +17,6 @@ import (
 	"runtime"
 	"sort"
 	"strings"
-	"syscall"
 	"time"
 )
 
@@ -131,13 +130,8 @@ func (m *Manager) preflight(composePath, targetVersion string) error {
 			return fmt.Errorf("检查 Host Updater 安装目录：%w", err)
 		}
 	}
-	var disk syscall.Statfs_t
-	if err := syscall.Statfs(m.config.BackupDir, &disk); err != nil {
-		return fmt.Errorf("检查备份磁盘空间：%w", err)
-	}
-	available := int64(disk.Bavail) * int64(disk.Bsize)
-	if available < 2<<30 {
-		return fmt.Errorf("备份目录可用空间不足 2 GiB：当前 %d MiB", available>>20)
+	if err := checkBackupDiskSpace(m.config.BackupDir); err != nil {
+		return err
 	}
 	if err := m.compose(composePath, targetVersion, 2*time.Minute, nil, "config", "--quiet"); err != nil {
 		return fmt.Errorf("目标 Compose 校验失败：%w", err)