fix(release): support built-in credentials and refresh release boundary
GitHub now creates approval-required PR workflows for GITHUB_TOKEN-authored
opened/synchronize/reopened events. Restore optional custom credentials and
cover prepare/publish without a separate secret. Record the verified 5.0.0
checkpoint, public 133-tool catalog and package update in the installation guide.
Assisted-by: Sakuya (gensokyo-skills:sakuya-checkpointed-execution)