Cloning on Windows with core.autocrlf=true converted
frontend/docker-entrypoint.d/20-basic-auth.sh to CRLF. Inside the container
the kernel read the shebang as /bin/sh\r, found no such interpreter, and
nginx crashed with exit 127 in a restart loop, so `docker compose up` never
produced a working web container.
- .gitattributes: LF for everything Linux executes or parses
- frontend/Dockerfile: sed strips CR at build time, covering checkouts made
before .gitattributes existed
