xuya227939/full-stack — reverse-engineered prompt

Build me a polished full stack web app starter that I can use to launch a real SaaS product quickly. I want it to have a modern landing page, login and signup, user accounts, a blog or content section for SEO, and clean pages that look ready to customize for different products.

Please wire it up with Supabase for auth and database, include API routes, and make payments work with Stripe, with Alipay support if it already fits the project. Add email sending for things like welcome emails or notifications. It should support multiple languages and be set up so I can deploy it without a huge refactor.

Use the existing Next.js and React setup in this repo, keep the code clean, and make sure the app runs locally with the documented env variables. If anything needs keys, leave clear placeholders and simple setup notes. Also run the basic checks and fix any obvious build or startup issues.