Replace GRUB with ZFSBootMenu bootloader

This is a major change that replaces the GRUB bootloader with ZFSBootMenu,
providing native ZFS boot environment support.

Key changes:
- EFI partition reduced from 1GB to 512MB (only holds ZFSBootMenu)
- EFI now mounts at /efi instead of /boot
- Kernel and initramfs live on ZFS root (enables snapshot boot with matching kernel)
- Downloads pre-built ZFSBootMenu EFI binary from get.zfsbootmenu.org
- Creates EFI boot entries for all disks in multi-disk configurations
- Syncs ZFSBootMenu to all EFI partitions for redundancy
- Sets org.zfsbootmenu:commandline on zroot/ROOT for kernel cmdline inheritance
- Sets bootfs pool property for default boot environment
- AMD GPU workarounds (pg_mask, cwsr_enable) added to kernel cmdline when AMD detected

Deleted GRUB snapshot tooling (no longer needed):
- custom/grub-zfs-snap
- custom/40_zfs_snapshots
- custom/zz-grub-zfs-snap.hook
- custom/zfs-snap-prune

Updated helper scripts:
- zfssnapshot: removed grub-zfs-snap call, shows ZFSBootMenu tip
- zfsrollback: removed grub-zfs-snap call, notes auto-detection

Tested configurations:
- Single disk installation
- 2-disk mirror (mirror-0)
- 3-disk RAIDZ1 (raidz1-0)
- All boot correctly with ZFSBootMenu

1 files changed, 0 insertions, 22 deletions

diff --git a/custom/zz-grub-zfs-snap.hook b/custom/zz-grub-zfs-snap.hook
deleted file mode 100644
index 8153b84..0000000
--- a/custom/zz-grub-zfs-snap.hook
+++ /dev/null
@@ -1,22 +0,0 @@
-[Trigger]
-Type = Package
-Operation = Upgrade
-Operation = Install
-Operation = Remove
-Target = linux-lts
-Target = linux-lts-headers
-Target = zfs-dkms
-Target = zfs-utils
-Target = grub
-
-[Trigger]
-Type = Path
-Operation = Install
-Operation = Upgrade
-Operation = Remove
-Target = usr/lib/modules/*/vmlinuz
-
-[Action]
-Description = Updating GRUB with ZFS snapshots...
-When = PostTransaction
-Exec = /usr/local/bin/grub-zfs-snap