Add Garand-Desktop flake with core boot module

Introduce a new flake for the Garand-Desktop host, including:
- top‑level flake.nix with inputs and outputs
- host config (default.nix) and modules:
  - hardware
  - home
  - system
  - packages
  - variables
- core boot module defining kernel and Limine loader styling
  with appimage support and plymouth enabled

flake.nix

@@ -0,0 +1,15 @@
+{
+  description = "GarandOS flake";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+
+    flake-parts.url = "github:hercules-ci/flake-parts";
+
+    import-tree.url = "github:vic/import-tree";
+  };
+
+  outputs = inputs: inputs.flake-parts.lib.mkFlake {
+    inherit inputs;
+  } (inputs.import-tree ./src);
+}