feat(attic): remove ESP partition and enable GRUB for legacy boot

- Remove the ESP partition configuration in `disko.nix` as it’s unnecessary for legacy BIOS setups.
- Enable GRUB bootloader and disable EFI settings in `default.nix` for compatibility with Hetzner cloud instances.

systems/x86_64-linux/attic/default.nix

@@ -1,4 +1,5 @@
 {
+  lib,
   ...
 }:
 {
@@ -23,6 +24,11 @@
     podman.dockerCompat = false;
   };
 
+  # Legacy BIOS boot (Hetzner cloud instance)
+  boot.loader.systemd-boot.enable = lib.mkForce false;
+  boot.loader.efi.canTouchEfiVariables = lib.mkForce false;
+  boot.loader.grub.enable = true;
+
   security.tpm2.enable = false;
   security.tpm2.abrmd.enable = false;