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/desktop/cosmic.nix

@@ -0,0 +1,11 @@
+{ config, pkgs, ... }: {
+  # Cosmic Desktop Environment (System76's new Rust-based DE)
+  services.desktopManager.cosmic.enable = true;
+  services.displayManager.cosmic-greeter.enable = true;
+  services.desktopManager.cosmic.xwayland.enable = true;
+  
+  # Cosmic-specific packages
+  environment.systemPackages = with pkgs; [
+    # Cosmic is still in development, most packages come with the DE
+  ];
+}