Initial shared NixOS modules

system/default/nix.nix

@@ -0,0 +1,56 @@
+{ ... }:
+{
+  # Nix package manager configuration
+  nix = {
+    settings = {
+      # Enable experimental features for modern Nix functionality
+      # - "nix-command": Enables the new unified 'nix' command interface
+      # - "flakes": Enables Nix flakes for reproducible and composable configurations
+      experimental-features = "nix-command flakes";
+
+      # Specify which users are allowed to run nix commands
+      allowed-users = [ "tb" ];
+
+      # Users who can act as trusted users (can override settings)
+      # Trusted users can use --option flags and import from derivations
+      trusted-users = [ "root" "tb" ];
+
+      # Show more lines of build output on failure
+      log-lines = 50;
+    };
+
+    # Automatic garbage collection configuration
+    # Helps manage disk space by cleaning up unused store paths
+    gc = {
+      # Enable automatic garbage collection
+      automatic = true;
+
+      # Delete store paths older than 30 days during garbage collection
+      options = "--delete-older-than 30d";
+    };
+
+    # Automatic store optimization configuration
+    # Reduces disk usage by hard-linking identical files in the Nix store
+    optimise = {
+      # Enable automatic store optimization
+      # This deduplicates files to save disk space
+      automatic = true;
+
+      # Run optimization weekly
+      dates = [ "weekly" ];
+    };
+  };
+
+  # Nixpkgs package collection configuration
+  nixpkgs = {
+    config = {
+      # Allow installation of packages with non-free licenses
+      # This includes proprietary software like Discord, Slack, etc.
+      # Without this, only free/open-source packages can be installed
+      allowUnfree = true;
+
+      # Allow packages marked as broken (use with caution)
+      #allowBroken = false;
+    };
+  };
+}