ignavia: cap GRUB generations to fit the 1 GiB ESP
/boot is only 1 GiB (disk.nix). Without configurationLimit, GRUB retains
every generation's kernel+initrd until the ESP fills, at which point the
bootloader install fails ("No space left on device") and deploys can't
finish. Keep the 10 most recent; older kernels get pruned automatically.
Assisted-by: Claude Code (claude-fable-5)