feat: disko OS-disk layout + nixos-anywhere install flow

- add disko input; jupiter partitions/formats OS disk declaratively
- hardware-configuration.nix carries kernel modules only (disko owns fileSystems)
- data disk stays a plain unformatted mount, out of disko
- vbox unchanged (virtualbox-image supplies its own disk)
- README: nixos-anywhere remote install + daily rebuild loop

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

jupiter/configuration.nix

@@ -1,9 +1,10 @@
 { config, pkgs, lib, ... }:
 
-# Real-host config: hardware + bootloader + shared services.
+# Real-host config: hardware + disk layout + bootloader + shared services.
 {
   imports = [
     ./hardware-configuration.nix
+    ./disk-config.nix          # disko: OS-disk partitions + filesystems
     ./services.nix
   ];
 
@@ -11,4 +12,12 @@
   # systemd-boot for UEFI. If ZimaBlade boots legacy/BIOS, switch to grub.
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
+
+  # ---- NAS data disk ----
+  # Existing data filesystem — mounted, NOT formatted (kept out of disko).
+  # Set the id from `ls -l /dev/disk/by-id` (or by-uuid). Adjust fsType.
+  # fileSystems."/mnt/data" = {
+  #   device = "/dev/disk/by-id/CHANGE-ME-data-disk";
+  #   fsType = "ext4";
+  # };
 }