Moves the two batch-runner handlers (--for-each-zone,
--for-each-tile) out of main.cpp into a new
cli_for_each.{hpp,cpp} module. Both substitute `{}` with the
iterated path (find -exec convention) and shell-escape every
token before passing to std::system. Exit code is the failure
count, capped at 255 so the shell can still see it.
main.cpp shrinks by 157 lines (2,964 to 2,807).
