feat(installer): add 'Install to disk' in Tools submenu

Copies the live system to a local disk via unsquashfs — no debootstrap,
no network required. Supports UEFI (GPT+EFI) and BIOS (MBR) layouts.

ISO:
- Add squashfs-tools, parted, grub-pc, grub-efi-amd64 to package list
- New overlay script bee-install: partitions, formats, unsquashfs,
  writes fstab, runs grub-install+update-grub in chroot

Go TUI:
- Settings → Tools submenu (Install to disk, Check tools)
- Disk picker screen: lists non-USB, non-boot disks via lsblk
- Confirm screen warns about data loss
- Runs with live progress tail of /tmp/bee-install.log
- platform/install.go: ListInstallDisks, InstallToDisk, findLiveBootDevice

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/config/package-lists/bee.list.chroot

@@ -18,6 +18,12 @@ qemu-guest-agent
 # SSH
 openssh-server
 
+# Disk installer
+squashfs-tools
+parted
+grub-pc
+grub-efi-amd64
+
 # Filesystem support for USB export targets
 exfatprogs
 exfat-fuse