The packaged changelog is now a recent-releases slice produced by
scripts/sync-changelog.sh (which gains a --check mode); also restore the
SECURITY.md contact line the version gate guards, and finish the stale
binary-name sweep (--bin codewhale examples, qa harness doc).
The /change command embeds this file into every binary via include_str!;
it now carries only recent releases (regenerated by scripts/sync-changelog.sh,
wired into the release checklist). The explicit-version test derives its
fixture versions from the embedded slice instead of hardcoding old ones.