Add zerombr and clearpart commands to ensure clean disk state before installation.
This prevents issues when reinstalling on previously partitioned disks by:
- Reinitializing invalid partition tables (zerombr)
- Removing all partitions from all disks (clearpart --all)
- Writing a fresh disk label (--initlabel)
This makes reinstallation reliable even on disks with previous installations,
while allowing users to override defaults via the GUI if needed.
nocode
