Add initial Nix flake configuration for PC and Laptop with Home Manager support

- Create flake.nix to define NixOS configurations for PC and Laptop
- Add README.md with setup instructions and layout overview
- Implement common NixOS settings in modules/common.nix
- Configure Home Manager for user-specific settings in home/users/user/home.nix
- Set up hardware configurations for both PC and Laptop
- Enable Home Manager integration in host configurations
- Introduce Zen Browser package definition

modules/common.nix

@@ -0,0 +1,61 @@
+{ config, lib, pkgs, ... }:
+{
+  nix = {
+    settings = {
+      experimental-features = [ "nix-command" "flakes" ];
+      auto-optimise-store = true;
+    };
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 14d";
+    };
+  };
+
+  time.timeZone = "UTC";
+
+  i18n = {
+    defaultLocale = "en_US.UTF-8";
+    extraLocaleSettings = {
+      LC_TIME = "en_US.UTF-8";
+      LC_MONETARY = "en_US.UTF-8";
+      LC_NUMERIC = "en_US.UTF-8";
+      LC_MEASUREMENT = "en_US.UTF-8";
+      LC_PAPER = "en_US.UTF-8";
+    };
+  };
+
+  console = {
+    keyMap = "us";
+    earlySetup = true;
+  };
+
+  networking.networkmanager.enable = true;
+
+  services.openssh = {
+    enable = true;
+    settings = {
+      PasswordAuthentication = false;
+      KbdInteractiveAuthentication = false;
+      PermitRootLogin = "no";
+    };
+  };
+
+  security.sudo.wheelNeedsPassword = false;
+
+  users.defaultUserShell = pkgs.bashInteractive; # change to zsh if preferred
+
+  environment.systemPackages = with pkgs; [
+    alakritty
+    # Custom Zen Browser package (defined in ../packages/zen-browser.nix)
+    (pkgs.callPackage ../packages/zen-browser.nix { inherit (pkgs) buildMozillaMach buildNpmPackage fetchFromGitHub lib fetchurl git pkg-config python3 vips runtimeShell writeScriptBin; })
+  ];
+
+  # Allow proprietary software if needed
+  nixpkgs.config = {
+    allowUnfree = true;
+  };
+
+  # Set the minimal stateVersion. When you upgrade, bump per host.
+  system.stateVersion = "24.05"; # do not change without reading the manual
+}