Initial NixOS flake-based multi-host setup

Add a NixOS system configuration using flakes, supporting multiple hosts (desktop, laptop, my-machine) with shared and per-host settings. Includes Home Manager integration, user-level and system-level package management, and example hardware configuration placeholders. Provides a README with setup instructions and a .gitignore for common Nix and editor artifacts.

hosts/laptop/hardware-configuration.nix

@@ -0,0 +1,34 @@
+# This file should be generated by running:
+# nixos-generate-config --show-hardware-config > hardware-configuration.nix
+#
+# Run this command on your LAPTOP to get the correct hardware configuration
+# Then copy the output here.
+
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports = [ ];
+
+  # PLACEHOLDER: Replace this entire file with your actual hardware configuration
+  # You can generate it by running the command mentioned above on your NixOS system
+  
+  boot.initrd.availableKernelModules = [ ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/nixos";
+    fsType = "ext4";
+  };
+
+  # Swap configuration
+  # swapDevices = [ ];
+
+  # CPU microcode updates (uncomment for your CPU)
+  # hardware.cpu.intel.updateMicrocode = true;
+  # hardware.cpu.amd.updateMicrocode = true;
+
+  # Laptop power management
+  powerManagement.cpuFreqGovernor = "powersave";
+}