detect.py listed .dockerfile/.makefile in SKIP_EXTENSIONS, but real
files are named Dockerfile/Makefile with no extension, so they fell
through to the content heuristic and came back compressible —
/caveman-compress Dockerfile overwrote a Dockerfile with caveman prose.
Add a basename guard (Dockerfile, Makefile, Jenkinsfile, Vagrantfile,
CMakeLists.txt, ...) checked before any extension rule — CMakeLists.txt
would otherwise ride the compressible .txt rule — and a shebang check
in the extensionless branch so executable scripts are always code.
Mirror synced to plugins/caveman (sync workflow only triggers on
SKILL.md changes, so scripts/ must ride along).
Fixes#600
