qt/qtbase — reverse-engineered prompt

I want this repo turned into a working local build of Qt Base so I can use it as the foundation for desktop C plus plus apps. Please set it up so the core, GUI, widgets, and network pieces build cleanly from source, with a simple default developer build that is easy to rerun.

If there are platform specific steps, make them clear and keep the flow practical for a normal developer on Linux or Windows. I would also like a quick sanity check at the end, like building and running one small example or test so we know the libraries actually work.

Please keep the changes minimal and in the style of the project. Add any small helper scripts or notes that make configuring, building, and testing easier, and explain how to do a clean rebuild. If the project already has a preferred configure path, use that instead of inventing something new. You can look up current Qt build docs online if you need to.