R-i-s-hi/ArchGen ? reverse-engineered prompt

Build me a web app called ArchGen that lets someone type in a project idea and instantly get a full software architecture plan.

I want it to show a recommended tech stack, a short explanation of why that setup makes sense, a suggested folder structure, a few API route ideas, and some future feature suggestions. It should let users save their generated projects, see their past ones later, copy the result as markdown, and export it as a clean PDF. I also want shareable links, with a public option and a restricted option for invited access.

Make it feel polished and easy to use, with a simple form for entering the idea, a results page that is easy to read, and a history area for old projects. Use a modern React app for the frontend and a Node and Express API for the backend, with database storage and AI based generation behind the scenes. If anything is unclear, check current docs online and make sensible choices.