Add build-modules.yml for Nix module dry-run workflow

dry_run.zsh

@@ -0,0 +1,28 @@
+#!/usr/bin/env zsh
+
+export NIX_CONFIG="experimental-features = nix-command flakes"
+
+echo "=== nix --version ==="
+nix --version
+echo
+
+configs=(
+  "nixos-local-wireguard-server"
+  "nixos-blank"
+  "nixos-songsheet"
+  "nixos-database"
+  "nixos-forgejo"
+  "nixos-teamspeak"
+  "nixos-traefik"
+  "nixos-build-machine"
+)
+
+if [[ -n "$1" ]]; then
+  configs=("$1")
+fi
+
+for config in "${configs[@]}"; do
+  echo "=== Dry-run: $config ==="
+  nix build --dry-run ".#nixosConfigurations.${config}.config.system.build.toplevel" || true
+  echo
+done