The .gitconfig at /home/hermes/.gitconfig was never read because the
hermes-agent service sets HOME=/var/lib/hermes. Git identity was already
fully covered by GIT_AUTHOR_* and GIT_COMMITTER_* env vars via .env.
Replace the dead .gitconfig's init.defaultBranch with the env var
GIT_INIT_DEFAULT_BRANCH (supported since Git 2.28).
