#1566 UPDATE.bat prints a PowerShell-incompatible command

Descripción

When UPDATE.bat detects an old repository history, it prints:

git branch pre-cleanup-backup && git stash push

This fails when copied into Windows PowerShell 5.1, which does not support && as a statement separator.

The recovery instructions should be compatible with PowerShell 5.1 as well.

PR #1568 fixes this