feat: initial NixOS home lab infrastructure setup

- Add modular flake-based NixOS configuration
- Implement GitOps foundation with CI/CD pipeline
- Create comprehensive documentation and branching strategy
- Add modular desktop environments (GNOME, Cosmic, Sway)
- Configure virtualization stack (Incus, Libvirt, Podman)
- Set up development tools and hardware-specific modules
- Establish user configuration with literate programming support

This commit represents the completion of Phase 1: Flakes Migration
with modular configuration, virtualization, and GitOps foundation.

modules/common/nix.nix

@@ -0,0 +1,36 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # Enable flakes and other experimental features
+  nix = {
+    settings = {
+      experimental-features = [ "nix-command" "flakes" ];
+      auto-optimise-store = true;
+      trusted-users = [ "root" "@wheel" ];
+      substituters = [
+        "https://cache.nixos.org/"
+        "https://nix-community.cachix.org"
+      ];
+      trusted-public-keys = [
+        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+      ];
+    };
+    
+    # Enable garbage collection
+    gc = {
+      automatic = true;
+      dates = "weekly";
+      options = "--delete-older-than 30d";
+    };
+
+    # Optimize store weekly
+    optimise = {
+      automatic = true;
+      dates = [ "03:45" ];
+    };
+  };
+
+  # Allow unfree packages
+  nixpkgs.config.allowUnfree = true;
+}