Wire the full pipeline into the binary: parse + validate the KDL buildfile,
discover extensions, bridge Lua, detect the C toolchain, and emit ./configure.
Adds the project's own stupid.kdl build file and a temp-dir-isolated self-host
integration test proving the generated configure + make rebuild the tool with
-std=c23. tests/run.sh tests 6+8 re-pin the interim 'accepted, no read' CLI
assertions to the wired 'missing buildfile -> exit 1' behavior.
