system: extract shared configuration from host configs

Extract duplicated configuration from gunter and magicman into shared
system modules. This eliminates ~116 lines of duplication and fixes a
malformed gdm.wayland config in magicman.

New shared modules:
- boot.nix: systemd-boot, EFI, common kernel params
- networking.nix: NetworkManager, nftables, firewall base
- hyprland.nix: System-level Hyprland and display manager
- xdg.nix: XDG session variables and portal setup
- nix-config.nix: Nix daemon settings, binary caches, trusted users
- nixpkgs-config.nix: allowUnfree and kernel packages default

Updated modules:
- locale.nix: Added timezone configuration

Benefits:
- Reduces duplication: net reduction of 53 lines
- Magicman gains custom cache substituters for faster builds
- Fixes malformed gdm.wayland config in magicman
- Both hosts use identical base configuration
- Host-specific config clearly stands out

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

hosts/magicman/configuration.nix

@@ -8,24 +8,13 @@
 
   # Bootloader stuff
   boot.kernelParams = [
-    "quiet"
-    "splash"
-    "rd.systemd.show_status=false"
     "acpi_backlight=native"
     "video=efifb:nobgrt"
     "loglevel=3"
     "rd.udev.log_level=3"
   ];
-  boot.kernelPackages = pkgs.linuxPackages_latest;
 
-  boot.loader.systemd-boot = {
-    enable = true;
-    configurationLimit = 3;
-  };
-
-  boot.loader.efi = {
-    canTouchEfiVariables = true;
-  };
+  boot.loader.systemd-boot.configurationLimit = 3;
 
   boot.initrd.systemd.enable = true;
   boot.plymouth = {
@@ -39,14 +28,6 @@
 
   # Networking stuff
   networking.hostName = "magicman"; # Define your hostname.
-  networking.networkmanager.enable = true;
-  networking.nftables.enable = true;
-  networking.firewall = {
-    enable = true;
-  };
-
-  # Set time stuff
-  time.timeZone = "Europe/Oslo";
 
   hardware = {
     enableRedistributableFirmware = true;
@@ -80,58 +61,11 @@
     };
   };
 
-  # Setup hyprland
-  services.xserver.enable = true;
-  services.displayManager.gdm.wayland = {
-    gdm.wayland = true;
-    lightdm.enable = false;
-  };
-  programs.hyprland = {
-    enable = true;
-    withUWSM = true;
-    xwayland.enable = true;
-    portalPackage = pkgs.xdg-desktop-portal-hyprland;
-  };
-
   # TRIM
   services.fstrim.enable = true;
 
-  # Setup common XDG env vars
-  environment.sessionVariables = rec {
-    XDG_CACHE_HOME = "$HOME/.cache";
-    XDG_CONFIG_HOME = "$HOME/.config";
-    XDG_DATA_HOME = "$HOME/.local/share";
-    XDG_STATE_HOME = "$HOME/.local/state";
-    XDG_BIN_HOME = "$HOME/.local/bin";
-    PATH = [ "${XDG_BIN_HOME}" ];
-  };
-
-  # Setup xdg portal
-  xdg.portal = {
-    enable = true;
-    xdgOpenUsePortal = true;
-    extraPortals = (
-      with pkgs;
-      [
-        # xdg-desktop-portal-hyprland
-        xdg-desktop-portal-gtk
-      ]
-    );
-  };
-
   programs.steam.enable = true;
 
-  # Enable flakes
-  nix.settings.experimental-features = [
-    "nix-command"
-    "flakes"
-  ];
-  nix.settings.trusted-users = [
-    "root"
-    "torjus"
-  ];
-
-  nixpkgs.config.allowUnfree = true;
   # Install system-wide packages
   environment.systemPackages = with pkgs; [
     vim