Add setup-git-auth.sh: idempotent, fail-silent script that primes the
git credential store from the vault Gitea token, scoped per-repo by the
actual origin host. Only seizes the helper from the prompting GCM
`manager` (leaves Mac osxkeychain alone); fast-path no-op once set.
Wire it into a backgrounded SessionStart hook and set
GIT_TERMINAL_PROMPT=0 / GCM_INTERACTIVE=Never in settings.json env so
no session on any machine can hang on a credential prompt.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
