refactor!: restructure and document configuration

shared/nixos/common.nix

@@ -0,0 +1,70 @@
+{ pkgs, nixpkgs, ... }:
+
+{
+  # Enable experimental features
+  nix.settings.experimental-features = [
+    "nix-command"
+    "flakes"
+  ];
+
+  # Optimize storage
+  nix.optimise.automatic = true;
+  nix.settings.auto-optimise-store = true;
+
+  # Pin the nix registry
+  nix.registry = {
+    nixpkgs.flake = nixpkgs;
+  };
+
+  # Allow unfree packages
+  nixpkgs.config.allowUnfree = true;
+
+  # Enable nh, a bundle of CLI utilities for NixOS
+  programs.nh = {
+    enable = true;
+
+    # Enable automatic garbage collection.
+    clean.enable = true;
+    clean.dates = "daily";
+    clean.extraArgs = "--keep-since 4d --keep 3";
+
+    flake = "/home/wizardlink/.system";
+  };
+
+  # Enable flatpak to all users.
+  services.flatpak.enable = true;
+
+  environment.systemPackages = with pkgs; [
+    ## Tools
+    # Utilities
+    bat
+    duf
+    fuseiso
+    lm_sensors
+    p7zip
+    tree
+    unrar
+    unzip
+    wget
+    zip
+
+    # File managing
+    sshfs
+    yazi
+
+    # Networking
+    gping
+    nmap
+
+    # Processes
+    (btop.override {
+      # AMD GPU support
+      rocmSupport = true;
+    })
+    killall
+
+    # Filter
+    fzf
+    ripgrep
+  ];
+}