refactor(nixos): extract shared modules, enable firewall, pin nixpkgs url

- Add common-nixos.nix (timezone, locale, git/fastfetch) imported by every
  NixOS host, and laptop.nix (systemd-boot, sway, dvorak, iwd, firewall)
  imported by X1 and MBP. Strip the nixos-generate-config boilerplate from
  both machine configs and reduce them to host-specific settings.
- Enable the firewall on the laptops (was disabled); X1 opens 22 next to
  its sshd.
- Pin nixpkgs input to github:nixos/nixpkgs/nixos-26.05 for consistency;
  lock rev unchanged (still b51242d).
- Drop unused module arguments.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

system/machine/MBP-Asahi/configuration.nix

@@ -1,94 +1,26 @@
-# Edit this configuration file to define what should be installed on
-# your system. Help is available in the configuration.nix(5) man page, on
-# https://search.nixos.org/options and in the NixOS manual (`nixos-help`).
-
-{
-  config,
-  lib,
-  pkgs,
-  ...
-}:
+# MacBook Pro (Apple Silicon, Asahi NixOS). Shared laptop options live in
+# ../../modules/laptop.nix; only host-specific settings are here.
+{ pkgs, ... }:
 
 {
   imports = [
-    # Include the results of the hardware scan.
     ./hardware-configuration.nix
   ];
 
-  # Use the systemd-boot EFI boot loader.
-  boot.loader.systemd-boot.enable = true;
+  # Asahi manages the EFI vars from macOS; do not touch them from NixOS.
   boot.loader.efi.canTouchEfiVariables = false;
 
-  networking.hostName = "Emma-Asahi"; # Define your hostname.
-  # Pick only one of the below networking options.
-  # networking.wireless.enable = true;  # Enables wireless support via wpa_supplicant.
-  # networking.networkmanager.enable = true;  # Easiest to use and most distros use this by default.
+  networking.hostName = "Emma-Asahi";
 
-  networking.wireless.iwd = {
-    enable = true;
-    settings.General.EnableNetworkConfiguration = true;
-  };
-
-  # Set your time zone.
-  time.timeZone = "Europe/London";
-
-  # Configure network proxy if necessary
-  # networking.proxy.default = "http://user:password@proxy:port/";
-  # networking.proxy.noProxy = "127.0.0.1,localhost,internal.domain";
-
-  # Select internationalisation properties.
-  i18n.defaultLocale = "en_GB.UTF-8";
-  console = {
-    #     font = "Lat2-Terminus16";
-    keyMap = "dvorak";
-    #   useXkbConfig = true; # use xkb.options in tty.
-  };
-
-  # Enable the X11 windowing system.
-  # services.xserver.enable = true;
-
-  features.swayDesktop.enable = true;
-
-  # Allow swaylock to authenticate (no fingerprint reader on this machine).
+  # No fingerprint reader on this machine; empty service still lets swaylock
+  # authenticate via password.
   security.pam.services.swaylock = { };
 
-  # Specify path to peripheral firmware files.
+  # Apple peripheral firmware (Wi-Fi/Bluetooth). The directory is gitignored and
+  # populated out-of-band -- see README.
   hardware.asahi.peripheralFirmwareDirectory = ../../modules/firmware;
 
-  # Configure keymap in X11
-  # services.xserver.xkb.layout = "us";
-  # services.xserver.xkb.options = "eurosign:e,caps:escape";
-
-  # Enable CUPS to print documents.
-  # services.printing.enable = true;
-
-  # Enable sound.
-  # services.pulseaudio.enable = true;
-  # OR
-  # services.pipewire = {
-  #   enable = true;
-  #   pulse.enable = true;
-  # };
-
-  # Enable touchpad support (enabled default in most desktopManager).
-  # services.libinput.enable = true;
-
-  # Define a user account. Don't forget to set a password with ‘passwd’.
-  # users.users.alice = {
-  #   isNormalUser = true;
-  #   extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
-  #   packages = with pkgs; [
-  #     tree
-  #   ];
-  # };
-
-  # programs.firefox.enable = true;
-
-  # List packages installed in system profile. To search, run:
-  # $ nix search wget
   environment.systemPackages = with pkgs; [
-    #   wget
-    git
     asahi-bless
     asahi-nvram
     asahi-btsync
@@ -98,47 +30,6 @@
     iptables
   ];
 
-  # Some programs need SUID wrappers, can be configured further or are
-  # started in user sessions.
-  # programs.mtr.enable = true;
-  # programs.gnupg.agent = {
-  #   enable = true;
-  #   enableSSHSupport = true;
-  # };
-
-  # List services that you want to enable:
-
-  # Enable the OpenSSH daemon.
-  # services.openssh.enable = true;
-
-  # Open ports in the firewall.
-  # networking.firewall.allowedTCPPorts = [ ... ];
-  # networking.firewall.allowedUDPPorts = [ ... ];
-  # Or disable the firewall altogether.
-  networking.firewall.enable = false;
-
-  # Copy the NixOS configuration file and link it from the resulting system
-  # (/run/current-system/configuration.nix). This is useful in case you
-  # accidentally delete configuration.nix.
-  #system.copySystemConfiguration = true;
-
-  # This option defines the first version of NixOS you have installed on this particular machine,
-  # and is used to maintain compatibility with application data (e.g. databases) created on older NixOS versions.
-  #
-  # Most users should NEVER change this value after the initial install, for any reason,
-  # even if you've upgraded your system to a new NixOS release.
-  #
-  # This value does NOT affect the Nixpkgs version your packages and OS are pulled from,
-  # so changing it will NOT upgrade your system - see https://nixos.org/manual/nixos/stable/#sec-upgrading for how
-  # to actually do that.
-  #
-  # This value being lower than the current NixOS release does NOT mean your system is
-  # out of date, out of support, or vulnerable.
-  #
-  # Do NOT change this value unless you have manually inspected all the changes it would make to your configuration,
-  # and migrated your data accordingly.
-  #
-  # For more information, see `man configuration.nix` or https://nixos.org/manual/nixos/stable/options#opt-system.stateVersion .
-  system.stateVersion = "25.05"; # Did you read the comment?
-
+  # See `man configuration.nix` / the stateVersion docs before changing.
+  system.stateVersion = "25.05";
 }