SaaS App Scaffold

Build a SaaS application with the following features:

1. Authentication — Email/password signup and login with email verification
2. User Dashboard — Overview of key metrics and recent activity
3. Settings Page — Profile editing, password change, notification preferences
4. Billing — Stripe integration with subscription management
5. Admin Panel — User management table with search, filter, and role assignment

Use a clean, modern design with a sidebar navigation. Include loading states, error boundaries, and empty states for all pages.