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>

flake.nix

@@ -3,23 +3,32 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
+    disko = {
+      url = "github:nix-community/disko";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
-  outputs = { self, nixpkgs, ... }@inputs:
+  outputs = { self, nixpkgs, disko, ... }@inputs:
     let
       system = "x86_64-linux";
     in
     {
       nixosConfigurations = {
         # Real host — install on the ZimaBlade.
+        # disko owns the OS-disk partitioning + filesystems (see disk-config.nix).
         jupiter = nixpkgs.lib.nixosSystem {
           inherit system;
           specialArgs = { inherit inputs; };
-          modules = [ ./jupiter/configuration.nix ];
+          modules = [
+            disko.nixosModules.disko
+            ./jupiter/configuration.nix
+          ];
         };
 
         # VirtualBox test image. Build the OVA with:
         #   nix build .#nixosConfigurations.jupiter-vbox.config.system.build.virtualBoxOVA
+        # NOTE: no disko here — the virtualbox-image module supplies the disk.
         jupiter-vbox = nixpkgs.lib.nixosSystem {
           inherit system;
           specialArgs = { inherit inputs; };