Dockerfile: pin dependency commits via ARG instead of unpinned git clone

All 5 Dockerfiles cloned libcmdplus/uuidplus/libnetplus/libhtmlpp/libhttppp/
libconfplus/libparitypp from git HEAD with no commit pin and no
cache-busting, so a normal docker build silently kept whatever was cloned
at the image's first-ever build indefinitely (confirmed: the libnetplus
clone line was last touched 2025-09-21, predating be9faab by 10 months).
Pin each dependency to a commit via ARG so bumping it is a visible diff
instead of frozen Docker layer cache.