fix: harden thothctl Windows safe I/O

tools/thothctl/internal/testsupport/symlink_windows.go

@@ -0,0 +1,14 @@
+//go:build windows
+
+package testsupport
+
+import (
+	"errors"
+	"os"
+
+	"golang.org/x/sys/windows"
+)
+
+func isSymlinkPrivilegeUnavailable(err error) bool {
+	return errors.Is(err, os.ErrPermission) || errors.Is(err, windows.ERROR_PRIVILEGE_NOT_HELD)
+}