refactor: move from den based to flake-parts based

modules/flake-parts.nix

@@ -0,0 +1,36 @@
+{
+  inputs,
+  config,
+  ...
+}:
+let
+  nixosModules = config.flake.modules.nixos;
+in
+{
+  imports = [ inputs.flake-parts.flakeModules.modules ];
+
+  systems = [ "x86_64-linux" ];
+
+  flake.nixosConfigurations = {
+    orion = inputs.nixpkgs.lib.nixosSystem {
+      specialArgs = { inherit inputs; };
+      modules = [ nixosModules.orion ];
+    };
+
+    polaris = inputs.nixpkgs.lib.nixosSystem {
+      specialArgs = { inherit inputs; };
+      modules = [ nixosModules.polaris ];
+    };
+
+    zenith = inputs.nixpkgs.lib.nixosSystem {
+      specialArgs = { inherit inputs; };
+      modules = [ nixosModules.zenith ];
+    };
+  };
+
+  perSystem =
+    { pkgs, ... }:
+    {
+      formatter = pkgs.nixfmt-tree;
+    };
+}