Helix Boot v0.6.4

Please update from v0.6.2 and v0.6.3. In those, Update from a PC without your local.toml removed Kaspersky Rescue Disk from a stick that had it: the tool is switched off as shipped, and the update took that as a reason to remove it. Fixed here.

Also new:

• Helix Boot is on the stick itself. Every stick gets a HelixBoot folder with HelixBoot.exe and HelixBoot.sh, so it can be updated, or its look changed, from any PC.
• An update says what it will do first. HelixBoot.exe shows what it will copy, remove and keep, and asks before writing.
• A new stick is named HelixBoot instead of Ventoy.

Added

• Helix Boot on the stick itself: every stick gets a HelixBoot folder with
  the latest released HelixBoot.exe and HelixBoot.sh and a short README, so
  it can be updated, or its look changed, from any PC without downloading
  anything first.
• An update says what it will do before it does it. HelixBoot.exe shows
  what Update stick will copy, remove and keep, and asks before writing
  when anything is copied or removed. helix sync --dry-run and
  helix unpack --dry-run end with the same summary.
• A new stick is named HelixBoot instead of Ventoy (stick_label under
  [settings]; "Ventoy" keeps Ventoy's own).
• tests/boot/boot_menu.py boots the menu in QEMU with every theme, on UEFI
  and BIOS, and checks each came up; CI runs it on every push and keeps the
  screenshots.

Fixed

• An update from a PC without your local.toml removed a tool that is switched
  off as shipped but that you had switched on (Kaspersky Rescue Disk): it took
  "off here" as a reason to remove it. Only a tool switched off by hand in that
  PC's own local.toml counts now.

Changed

• A file on the stick that hasn't changed isn't written again on every
  refresh, and one that is in use (the app updating the stick from the stick,
  on Windows) no longer stops the run: it is replaced next time.