Initial NixOS flake-based multi-host setup

Add a NixOS system configuration using flakes, supporting multiple hosts (desktop, laptop, my-machine) with shared and per-host settings. Includes Home Manager integration, user-level and system-level package management, and example hardware configuration placeholders. Provides a README with setup instructions and a .gitignore for common Nix and editor artifacts.

system/common.nix

@@ -0,0 +1,71 @@
+{ config, pkgs, ... }:
+
+{
+  # Common system configuration shared across all machines
+  
+  # Bootloader
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+
+  # Networking
+  networking.networkmanager.enable = true;
+
+  # Timezone and locale
+  time.timeZone = "Europe/London";
+  i18n.defaultLocale = "en_US.UTF-8";
+  i18n.extraLocaleSettings = {
+    LC_ADDRESS = "en_US.UTF-8";
+    LC_IDENTIFICATION = "en_US.UTF-8";
+    LC_MEASUREMENT = "en_US.UTF-8";
+    LC_MONETARY = "en_US.UTF-8";
+    LC_NAME = "en_US.UTF-8";
+    LC_NUMERIC = "en_US.UTF-8";
+    LC_PAPER = "en_US.UTF-8";
+    LC_TELEPHONE = "en_US.UTF-8";
+    LC_TIME = "en_US.UTF-8";
+  };
+
+  # Enable sound
+  hardware.pulseaudio.enable = false;
+  security.rtkit.enable = true;
+  services.pipewire = {
+    enable = true;
+    alsa.enable = true;
+    alsa.support32Bit = true;
+    pulse.enable = true;
+    jack.enable = true;
+  };
+
+  # Enable CUPS for printing
+  services.printing.enable = true;
+
+  # Enable OpenGL
+  hardware.graphics = {
+    enable = true;
+    enable32Bit = true;
+  };
+
+  # System-wide packages
+  environment.systemPackages = with pkgs; [
+    vim
+    wget
+    curl
+    git
+    htop
+    neofetch
+    unzip
+    zip
+  ];
+
+  # Enable flakes
+  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+
+  # Allow unfree packages
+  nixpkgs.config.allowUnfree = true;
+
+  # Enable networking
+  networking.firewall.enable = true;
+
+  # System state version
+  system.stateVersion = "25.05";
+}