v0.5.1

Fixed

• scripts/release.sh is now a real dry-run: a preview (without --yes) no
  longer edits the tracked files in place. It used to flip the CHANGELOG header
  and bump VERSION/README on disk, leaving the tree dirty (and no [Unreleased]
  header for a second pass) — so the very --yes the dry-run pointed you to
  aborted on the script's own clean-tree precondition. The preview now diffs the
  proposed edits against the current files and writes nothing until --yes.
• CI is green on GitHub Actions again: the bash/zsh doctor parity test now
  pins TERM (runners leave it unset, where bash defaults to dumb and zsh
  does not), with two runner-only test failures also fixed. (0.5.0's tag CI was
  red, so its release job was skipped and no 0.5.0 GitHub Release exists — 0.5.1
  is the first green-CI tag since.)