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";
+  # };
 }

jupiter/disk-config.nix

@@ -0,0 +1,42 @@
+{ ... }:
+
+# Declarative OS-disk layout (disko). UEFI: GPT with an ESP + ext4 root.
+# disko both PARTITIONS/FORMATS this disk and generates the NixOS
+# `fileSystems.*` entries, so hardware-configuration.nix must NOT define
+# fileSystems for "/" or "/boot".
+#
+# ⚠️  This disk is WIPED on install. Set `device` to the OS disk ONLY.
+#     Your NAS data disk is NOT listed here — keep it out of disko so it is
+#     never formatted; mount it as a plain read-write fileSystem instead
+#     (see configuration.nix, /mnt/data).
+#
+# Find the stable id:  ls -l /dev/disk/by-id   (use by-id, never /dev/sdX)
+{
+  disko.devices.disk.os = {
+    type = "disk";
+    device = "/dev/disk/by-id/CHANGE-ME-os-disk";
+    content = {
+      type = "gpt";
+      partitions = {
+        ESP = {
+          size = "512M";
+          type = "EF00";
+          content = {
+            type = "filesystem";
+            format = "vfat";
+            mountpoint = "/boot";
+            mountOptions = [ "umask=0077" ];
+          };
+        };
+        root = {
+          size = "100%";
+          content = {
+            type = "filesystem";
+            format = "ext4";
+            mountpoint = "/";
+          };
+        };
+      };
+    };
+  };
+}

jupiter/hardware-configuration.nix

@@ -1,14 +1,13 @@
-# PLACEHOLDER — do not use as-is.
+# PLACEHOLDER — replace on the real machine.
 #
-# Generate the real file ON the ZimaBlade after booting the NixOS installer:
+# disko (disk-config.nix) owns the OS-disk filesystems, so this file should
+# only carry kernel modules + platform. Get the real values from the target:
 #
-#   sudo nixos-generate-config --root /mnt
+#   # during install, or via nixos-anywhere --generate-hardware-config:
+#   sudo nixos-generate-config --no-filesystems --root /mnt
 #
-# then copy /mnt/etc/nixos/hardware-configuration.nix over this file.
-# It contains machine-specific disk UUIDs, filesystems, and kernel modules.
-#
-# The block below is a minimal example so `nix flake check` does not fail on a
-# workstation. REPLACE it entirely with the generated output.
+# `--no-filesystems` omits the fileSystems.* blocks (disko provides them).
+# Copy the generated file over this one. Keep the imports/kernel-module lines.
 { config, lib, pkgs, modulesPath, ... }:
 
 {
@@ -19,22 +18,8 @@
   boot.kernelModules = [ ];
   boot.extraModulePackages = [ ];
 
-  # Example root — replace UUID with real value from generated config.
-  fileSystems."/" = {
-    device = "/dev/disk/by-label/nixos";
-    fsType = "ext4";
-  };
-
-  fileSystems."/boot" = {
-    device = "/dev/disk/by-label/BOOT";
-    fsType = "vfat";
-  };
-
-  # Example NAS data mount. Point at your storage disk/pool.
-  # fileSystems."/mnt/data" = {
-  #   device = "/dev/disk/by-label/data";
-  #   fsType = "ext4";
-  # };
+  # NO fileSystems here — disko defines "/" and "/boot" (see disk-config.nix).
+  # The NAS data mount lives in configuration.nix.
 
   swapDevices = [ ];