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

home/users/user/home.nix

@@ -0,0 +1,17 @@
+{ config, pkgs, ... }:
+{
+  home.username = "user"; # set by flake variable in system configs; keep consistent
+  home.homeDirectory = "/home/user";
+
+  # Set once on first deploy; bump if you intentionally accept breaking changes
+  home.stateVersion = "24.05";
+
+  programs.home-manager.enable = true;
+
+  programs.bash.enable = true;
+  programs.starship = { enable = true; enableBashIntegration = true; };
+
+  home.packages = with pkgs; [
+    fastfetch
+  ];
+}