fix uefi issue in iso boot

hosts/buildbox/iso.nix

@@ -10,8 +10,15 @@
     ../iso/default.nix
   ];
 
+  # Enable BIOS (MBR) boot for SeaBIOS compatibility in Proxmox
   boot.loader.grub.enable = lib.mkDefault true;
   boot.loader.grub.devices = ["nodev"];
+  boot.loader.grub.efiSupport = false;
+  boot.loader.grub.forceEfiBootloaderId = false;
+
+  # Build ISO with both BIOS and UEFI support
+  isoImage.makeEfiBootable = true;
+  isoImage.makeBiosBootable = true;
 
   iso.extraPackages = with pkgs; [btrfs-progs];
   iso.diskoConfig = ./disko-config.nix;