v0.2.3

Added

• post-create.py warns loudly when no git identity is configured. The
  sandbox inherits user.name/user.email from the read-only host
  ~/.gitconfig; if that was empty/broken at build time, git commit failed
  mid-session with a cryptic "Author identity unknown" and couldn't be fixed
  from inside. Container creation now flags it last with the host-side fix.
  (post-create.py)