Add build-glove80 script

Instead of running NixOS in Docker, I can build the firmware natively as
I'm running NixOS.

nix/home/opdavies/default.nix

@@ -51,6 +51,7 @@ in
       with pkgs;
       [
         brave
+        build-glove80
         discord
         gimp
         gscan2pdf

nix/pkgs/build-glove80.nix

@@ -0,0 +1,41 @@
+{ pkgs, ... }:
+
+pkgs.writeShellApplication {
+  name = "build-glove80";
+
+  runtimeInputs = with pkgs; [
+    cachix
+    git
+    nix
+  ];
+
+  text = ''
+    BRANCH="''${1:-main}"
+    SRC_DIR="''${PWD}/src"
+    CONFIG_DIR="''${PWD}/config"
+    NIX_FILE="''${CONFIG_DIR}/default.nix"
+
+    # Ensure cachix is configured
+    echo "Using moergo-glove80-zmk-dev cache"
+    cachix use moergo-glove80-zmk-dev
+
+    # Clone or update the ZMK repository
+    if [ ! -d "$SRC_DIR" ]; then
+      echo "Cloning ZMK repository into ./src..."
+      git clone https://github.com/moergo-sc/zmk "$SRC_DIR"
+    else
+      echo "Updating ZMK repository in ./src..."
+      git -C "$SRC_DIR" fetch --all
+    fi
+
+    # Checkout the specified branch or tag
+    echo "Checking out branch/tag: $BRANCH in ./src"
+    git -C "$SRC_DIR" checkout -q --detach "$BRANCH"
+
+    # Build firmware using Nix
+    echo "Building firmware from: $NIX_FILE"
+    nix-build "$NIX_FILE" --arg firmware "import ''${SRC_DIR}/default.nix {}" -j2 -o ./glove80.uf2 --show-trace
+
+    echo "Firmware built successfully: $(realpath ./glove80.uf2)"
+  '';
+}

nix/pkgs/default.nix

@@ -4,6 +4,8 @@ let
   inherit (pkgs) callPackage;
 in
 {
+  build-glove80 = callPackage ./build-glove80.nix { };
+
   vimPlugins = prev.vimPlugins // {
     conf-vim = callPackage ./vim-plugins/conf-vim.nix { };
     edit-alternate-vim = callPackage ./vim-plugins/edit-alternate-vim.nix { };