A plain `docker build .` now stamps the version into bsdaily: the
VERSION build argument when one is given, otherwise `git describe
--tags --always` of the .git in the build context. The build fails if
the context carries .git and no version comes out. A host `make` build
stamps the same `git describe` value. bsdaily prints it with --version.
The new .dockerignore is the canonical copy, which keeps .git/config
out of the build context. script/docker is replaced with the canonical
copy, which passes the version it derives on the host.
Model: opus-5-5
sneak