* fix(repos): preserve unknown Git availability
* fix(git): distinguish binary absence from missing cwd on spawn ENOENT
Node reports ENOENT for both a missing git binary and a missing working directory
during spawn. The fix checks specifically for spawn syscall, then verifies the cwd
exists to disambiguate. This prevents reporting "no Git" when the error is actually
a missing working directory. Centralizes probe logic in a reusable function; other
failures cause rejection so callers preserve the unknown status instead of collapsing
to false.