Rearrange nixos system config

hosts/nixos/system-default.nix

@@ -0,0 +1,64 @@
+{ config, pkgs, ... }:
+
+{
+  # Common NixOS system configuration shared across all hosts
+
+  # Time zone and localization
+  time.timeZone = "Europe/Copenhagen";
+  i18n.defaultLocale = "en_US.UTF-8";
+
+  # Enable zsh system-wide (required when set as user shell)
+  programs.zsh.enable = true;
+
+  # Enable bandwhich network monitoring tool
+  programs.bandwhich.enable = true;
+
+  # Enable experimental nix features
+  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+
+  # Allow unfree packages globally
+  nixpkgs.config.allowUnfree = true;
+
+  # Basic SSH configuration
+  services.openssh = {
+    enable = true;
+    settings = {
+      PasswordAuthentication = false;
+      KbdInteractiveAuthentication = false;
+      AcceptEnv = "LANG LC_* TERM COLORTERM TMUX TMUX_PANE";
+    };
+  };
+
+  # Common user configuration
+  users.users.yanlin = {
+    isNormalUser = true;
+    description = "yanlin";
+    shell = pkgs.zsh;
+  };
+
+  # Enable sudo for wheel group without password
+  security.sudo.wheelNeedsPassword = false;
+
+  # Common system packages
+  environment.systemPackages = with pkgs; [
+    # Essential command-line tools
+    vim
+    git
+    htop
+    curl
+    wget
+    rsync
+    tmux
+    tree
+    lsof
+    tcpdump
+    iotop
+    
+    # Shell and system management
+    zsh
+    home-manager
+  ];
+
+  # Default system state version
+  system.stateVersion = "24.05";
+}