pallets/flask ? reverse-engineered prompt

Build me a lightweight Python web framework for making small web apps fast, but flexible enough to grow into bigger ones. I want it to feel simple for beginners, where I can create an app object, add routes with decorators, return plain text or HTML, and run a local development server with a simple command. It should handle the basics like requests, responses, URL routing, and rendering templates, without forcing a heavy project structure or too many built in opinions.

Please make it feel polished like a real framework, with clear docs, a tiny hello world example, and tests for the core behavior. Keep the code organized and easy to extend later with third party add ons. Include the normal developer setup so I can install it, run the tests, and start an example app quickly. If anything is unclear, look up current docs online and follow normal Python web framework conventions.