tq-systems/ci-meta-tq — reverse-engineered prompt

I want this repo turned into a clean, reproducible Yocto workspace for TQ Systems ARM boards on the scarthgap branch. Make it easy for someone to clone it with submodules, run one setup command, choose a config like mainline, imx, ti, or ls, and then see which machines are available.

The setup should support creating a new build directory, returning to an existing one, building images for all supported machines from a chosen config, and filling a local source mirror for offline builds. Please keep the helper scripts and sample config templates clear and practical, and make sure the docs explain the required tools, how MACHINE and DISTRO can be overridden, and how local site settings like shared downloads and sstate can be reused.

Also make the branch and submodule sync steps obvious, and clearly warn about the demo security defaults so nobody ships an image with empty root password or root ssh access by accident. Check current Yocto docs online if you need to.