dws upgrade registered no --dry-run flag and never read the global one,
so --dry-run fell through to runUpgrade and performed a real, irreversible
upgrade (download + replace binary). This contradicts the flag's documented
contract (预览操作内容，不实际执行).
Resolve the target release and platform asset (so a missing build / 'already
latest' is still reported), then render the planned 1-5 steps and return
before any side effect: no backup, no download, no replace. Advertise
--dry-run in the command examples.
Fixes#364
GoReleaser cross-compiles darwin/arm64 binaries on ubuntu-latest with no
codesign step. macOS 11+ on Apple Silicon requires at least an ad-hoc
signature; unsigned arm64 binaries are SIGKILL'd by amfid on first exec,
which surfaces as `signal: killed` and aborts `dws upgrade` at the
"解压并验证" step.
Two layers of fix:
1. Release-side: post-goreleaser.sh now unpacks each dws-darwin-*.tar.gz,
applies an ad-hoc signature (codesign locally, rcodesign in CI),
deterministically repacks, and rewrites the matching line in
checksums.txt. release.yml installs rcodesign 0.27.0 before
GoReleaser runs.
2. Client-side self-heal: validateNewBinary detects `signal: killed` on
darwin and retries once after running `codesign --force --sign -` and
clearing com.apple.quarantine. Future releases stay functional even
if the signing step is ever skipped.
Verified end-to-end: stripped a real dws binary → exec exits 137 →
validateNewBinary recovers → final binary shows Signature=adhoc and runs.
Jackjin