refactor: fold host-only modules into the hosts

- argon owns its gpu settings, calibre and the luks drives, now generated from one table
- claudecode.nix is gone, claude-code lives in packages.nix
- home-manager options live next to the home-manager wiring in flake.nix
- settings.nix: one nix block, extra-substituters instead of repeating the cache.nixos.org defaults
- README: current layout

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

modules/nixos/calibre.nix

@@ -1,8 +0,0 @@
-{ pkgs, ... }:
-
-{
-  # install calibre for ebook management and kobo syncing
-  environment.systemPackages = with pkgs; [
-    calibre
-  ];
-}

modules/nixos/claudecode.nix

@@ -1,7 +0,0 @@
-{ pkgs, ... }:
-
-{
-  environment.systemPackages = with pkgs; [
-    claude-code
-  ];
-}

modules/nixos/drives.nix

@@ -1,45 +0,0 @@
-# Add encrypted drives to argon
-
-{
-  # copy keyfiles into initrd to make them available during early boot
-  boot.initrd.secrets = {
-    "/etc/nixos/keys/data1.key" = "/etc/nixos/keys/data1.key";
-    "/etc/nixos/keys/data2.key" = "/etc/nixos/keys/data2.key";
-    "/etc/nixos/keys/nvmecache.key" = "/etc/nixos/keys/nvmecache.key";
-  };
-
-  # decrypt data drives with keyfiles for argon
-  boot.initrd.luks.devices = {
-    "data1" = {
-      device = "/dev/disk/by-uuid/dfae62cc-bad1-4879-bf9a-461bde833625";
-      keyFile = "/etc/nixos/keys/data1.key";
-    };
-    "data2" = {
-      device = "/dev/disk/by-uuid/8312edae-9247-481b-a313-52a7f848f027";
-      keyFile = "/etc/nixos/keys/data2.key";
-    };
-    "nvmecache" = {
-      device = "/dev/disk/by-uuid/2352250e-4ebe-4f9a-bf66-0d4aaa961bd8";
-      keyFile = "/etc/nixos/keys/nvmecache.key";
-    };
-  };
-
-  # mount decrypted filesystems
-  fileSystems."/mnt/data1" = {
-    device = "/dev/mapper/data1";
-    fsType = "ext4";
-    options = [ "nofail" ];
-  };
-
-  fileSystems."/mnt/data2" = {
-    device = "/dev/mapper/data2";
-    fsType = "ext4";
-    options = [ "nofail" ];
-  };
-
-  fileSystems."/mnt/nvmecache" = {
-    device = "/dev/mapper/nvmecache";
-    fsType = "ext4";
-    options = [ "nofail" ];
-  };
-}

modules/nixos/graphics.nix

@@ -1,17 +0,0 @@
-{ pkgs, ... }:
-
-{
-  # enable amd GPU acceleration (mesa, vulkan, egl)
-  hardware.graphics = {
-    enable = true;
-    enable32Bit = true;
-  };
-
-  # install amdgpu_top
-  environment.systemPackages = with pkgs; [
-    amdgpu_top
-  ];
-
-  # add amdgpu to the initrd for plymouth
-  hardware.amdgpu.initrd.enable = true;
-}

modules/nixos/settings.nix

@@ -1,31 +1,25 @@
 {
   nix = {
-    # nix settings
     settings = {
-      # enable flakes and nix-command
       experimental-features = [
         "nix-command"
         "flakes"
       ];
-      # auto-optimize my nix-store
       auto-optimise-store = true;
-      # use all cores
+      # parallel builds, each using all cores
       max-jobs = "auto";
-      # use all available cores per job
       cores = 0;
-      # add trusted substituters (binary caches)
-      substituters = [
-        "https://cache.nixos.org"
-        "https://nix-community.cachix.org"
-      ];
-      # add keys
-      trusted-public-keys = [
-        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+      # cache.nixos.org is the default, these come on top
+      extra-substituters = [ "https://nix-community.cachix.org" ];
+      extra-trusted-public-keys = [
         "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
       ];
+      trusted-users = [
+        "root"
+        "@wheel"
+      ];
     };
 
-    # enable automatic garbage collection
     gc = {
       automatic = true;
       dates = "weekly";
@@ -33,20 +27,9 @@
     };
   };
 
-  # add trusted users (able to modify the nix store)
-  nix.settings.trusted-users = [
-    "root"
-    "@wheel"
-  ];
-
-  # allow unfree packages (steam, protonvpn, discord, etc.)
+  # steam, protonvpn, discord, etc.
   nixpkgs.config.allowUnfree = true;
 
   # links /libexec from derivations to /run/current-system/sw
   environment.pathsToLink = [ "/libexec" ];
-
-  # enable home-manager globally
-  home-manager.useGlobalPkgs = true;
-  home-manager.useUserPackages = true;
-  home-manager.backupCommand = "mv -f {file} {file}.hm-bak-$(date +%Y%m%d%H%M%S)";
 }