move some nixos configuration to ./nixos/modules and ./nixos/configurations. try to find a good arch to conbine home-manager and nixos modules.

nixos/modules/default.nix

@@ -0,0 +1,30 @@
+{
+  inputs,
+  outputs,
+  pkgs,
+  ...
+}:
+{
+  imports =
+    (with inputs; [
+      niri-flake.nixosModules.niri
+      nixos-cosmic.nixosModules.default
+      home-manager.nixosModules.home-manager
+      dae.nixosModules.dae
+    ])
+    ++ [
+      ./nix.nix
+    ];
+
+  config = {
+    nixpkgs = {
+      overlays =
+        (with outputs; [
+          overlays.modifications
+        ])
+        ++ (with inputs; [
+          niri-flake.overlays.niri
+        ]);
+    };
+  };
+}

nixos/modules/nix.nix

@@ -0,0 +1,45 @@
+{
+  inputs,
+  outputs,
+  pkgs,
+  lib,
+  ...
+}:
+{
+  config = {
+    nix = {
+      nixPath = [ "nixpkgs=${inputs.nixpkgs}" ];
+      settings = {
+        inherit (outputs.nix.settings) substituters;
+        trusted-users = [
+          "root"
+          "@wheel"
+        ];
+        trusted-public-keys = [
+          "cosmic.cachix.org-1:Dya9IyXD4xdBehWjrkPv6rtxpmMdRel02smYzA85dPE="
+          "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+        ];
+        auto-optimise-store = lib.mkDefault true;
+        experimental-features = [
+          "nix-command"
+          "flakes"
+        ];
+        warn-dirty = false;
+        system-features = [
+          "kvm"
+          "big-parallel"
+        ];
+        use-xdg-base-directories = true;
+        builders-use-substitutes = true;
+      };
+      package = pkgs.nix;
+      registry.sys = lib.mkDefault {
+        from = {
+          type = "indirect";
+          id = "sys";
+        };
+        flake = inputs.nixpkgs;
+      };
+    };
+  };
+}