fix(release): ignore CI scratch .artifacts dir so publish-existing clean-worktree assertion passes (#1150) (#1285)

The v0.44.0-beta.1 publish run (autoflow-release.yml, run 33734627360)
failed after all release-tier gates passed: the workflow downloads the
authorizing PR-CI evidence artifact into .artifacts/pr-ci/, and
assertCleanWorktree rejected the untracked .artifacts/ dir
('Refusing release from a dirty worktree: ?? .artifacts/').

.artifacts/ is CI scratch, never a release input, so it belongs in the
root-local scratch artifacts ignore section alongside /.tmp/.

Co-authored-by: DevBot <devbot@openelement.dev>

Author: SisyphusZheng

.gitignore

@@ -125,3 +125,5 @@ examples/deno-desktop-mastodon/stress-report.json
 # Root-local media/agent scratch artifacts (never release inputs)
 /.tmp/
 /.tmp-*
+# Release workflow (autoflow-release.yml) PR-CI evidence download dir: CI scratch, never a release input
+/.artifacts/