Add initial Nix flake configuration for PC and Laptop with Home Manager support

- Create flake.nix to define NixOS configurations for PC and Laptop
- Add README.md with setup instructions and layout overview
- Implement common NixOS settings in modules/common.nix
- Configure Home Manager for user-specific settings in home/users/user/home.nix
- Set up hardware configurations for both PC and Laptop
- Enable Home Manager integration in host configurations
- Introduce Zen Browser package definition

hosts/laptop/hardware-configuration.nix

@@ -0,0 +1,19 @@
+# NOTE: Replace with the actual generated hardware config from the laptop.
+# Generate on the laptop with:
+#   sudo nixos-generate-config --show-hardware-config > hardware-configuration.nix
+{ config, lib, pkgs, modulesPath, ... }:
+{
+  imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+
+  boot.initrd.availableKernelModules = [ "xhci_pci" "ahci" "nvme" "usbhid" "sr_mod" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ "kvm-intel" ];
+  boot.extraModulePackages = [ ];
+
+  fileSystems."/" =
+    { device = "/dev/disk/by-uuid/11111111-1111-1111-1111-111111111111";
+      fsType = "ext4";
+    };
+
+  swapDevices = [ ];
+}