add a nix dev shell and helper script to start it up

build-and-run.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+pnpm install
+pnpm build
+cd apps/web
+pnpm preview

flake.nix

@@ -0,0 +1,31 @@
+{
+  description = "Helius Airship PNPM dev shell";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = { self, nixpkgs, ... }:
+    let
+      system = "x86_64-linux"; # adjust if on macOS
+      pkgs = import nixpkgs { inherit system; };
+    in
+    {
+      # This is the key: devShells.<system>.default
+      devShells = {
+        "${system}" = {
+          default = pkgs.mkShell {
+            buildInputs = [
+              pkgs.nodejs
+              pkgs.pnpm
+              pkgs.git
+            ];
+
+            shellHook = ''
+              echo "Welcome to Helius Airship PNPM dev shell!"
+              echo "Node version: $(node -v)"
+              echo "PNPM version: $(pnpm -v)"
+            '';
+          };
+        };
+      };
+    };
+}