Scaffold nikita-nixos host

Add a second nixosConfigurations entry for a friend's machine running
Plasma 6 + SDDM. The hardware-configuration.nix is a placeholder; it
must be replaced with the output of nixos-generate-config on the
actual hardware before installing. Git identity in hosts/nikita-nixos/
home.nix is also a placeholder.

hosts/nikita-nixos/default.nix

@@ -0,0 +1,25 @@
+{ ... }:
+
+{
+  imports = [
+    ./hardware-configuration.nix
+
+    # shared
+    ../../system/boot.nix
+    ../../system/networking.nix
+    ../../system/locale.nix
+    ../../system/fonts.nix
+    ../../system/nix.nix
+    ../../system/ssh.nix
+    ../../system/programs.nix
+    ../../system/packages.nix
+
+    # nikita-only
+    ../../system/plasma.nix
+    ../../system/display-managers/sddm.nix
+    ../../system/users/nikita.nix
+  ];
+
+  networking.hostName = "nikita-nixos";
+  system.stateVersion = "26.05";
+}

hosts/nikita-nixos/hardware-configuration.nix

@@ -0,0 +1,24 @@
+{ lib, modulesPath, ... }:
+
+# Placeholder hardware-configuration. Replace with the file generated on
+# Nikita's actual machine via `nixos-generate-config --root /mnt` before
+# building or installing.
+{
+  imports = [
+    (modulesPath + "/installer/scan/not-detected.nix")
+  ];
+
+  boot.initrd.availableKernelModules = [ ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/PLACEHOLDER-ROOT";
+    fsType = "ext4";
+  };
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+}

hosts/nikita-nixos/home.nix

@@ -0,0 +1,24 @@
+{ ... }:
+
+{
+  imports = [
+    ../../home/zsh.nix
+    ../../home/fonts.nix
+    ../../home/yazi.nix
+    ../../home/symlinks.nix
+    ../../home/packages-base.nix
+  ];
+
+  home.username = "nikita";
+  home.homeDirectory = "/home/nikita";
+  home.stateVersion = "26.05";
+
+  # TODO: replace with Nikita's actual git identity before first use
+  programs.git = {
+    enable = true;
+    settings.user = {
+      name = "Nikita";
+      email = "nikita@example.com";
+    };
+  };
+}