replace with real hardware configs

nix/hosts/common.nix

@@ -3,6 +3,16 @@
 {
   system.stateVersion = "26.05";
 
+  # Bootloader. The disko layout (hardware-configurations/disk-config.nix) lays
+  # down both a BIOS-boot (EF02) partition and an ESP mounted at /boot, so grub
+  # works whether the VM firmware is legacy BIOS or UEFI. disko fills in
+  # boot.loader.grub.devices from the EF02 partition; we just enable grub here.
+  boot.loader.grub = {
+    enable = true;
+    efiSupport = true;
+    efiInstallAsRemovable = true;
+  };
+
   nix.settings = {
     experimental-features = [ "nix-command" "flakes" ];
     trusted-users = [ "@wheel" "deploy" ];