build(saas-demo): add @playwright/test devDependency for smoke tests

Author: mxmzb

examples/showcases/banking/package.json

@@ -42,6 +42,7 @@
     "zod": "^3.25.76"
   },
   "devDependencies": {
+    "@playwright/test": "^1.59.1",
     "@types/node": "^20",
     "@types/react": "^18",
     "@types/react-dom": "^18",