Update Playwright + Use Nix (#311)

* use nix for execution

* update setup instructions

* headless

* headless via xvfb-run

flake.nix

@@ -0,0 +1,40 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+    flake-utils = {
+      url = "github:numtide/flake-utils";
+    };
+  };
+
+  outputs =
+    { nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+      in
+      {
+        devShell = pkgs.mkShell {
+          nativeBuildInputs = with pkgs; [
+            nodejs
+            playwright-driver.browsers
+            typescript
+            playwright-test
+
+            # fixes "waiting until load" issue compared to
+            # setting headless in config.json
+            xvfb-run
+          ];
+
+          shellHook = ''
+            export PLAYWRIGHT_BROWSERS_PATH=${pkgs.playwright-driver.browsers}
+            export PLAYWRIGHT_SKIP_VALIDATE_HOST_REQUIREMENTS=true
+            npm i
+            npm run build
+          '';
+        };
+      }
+    );
+}