fix(release): sync 2.5.7 with PyPI + safer release workflows

[abdulgeek]

Summary

• Align master package metadata with PyPI cost-katana==2.5.7 (setup.py, __version__, User-Agent, CHANGELOG).
• Auto Release: workflow_dispatch only; Twine runs only after commit + tag push succeed (no more PyPI-without-Git drift). Optional repo secret RELEASE_PUSH_TOKEN (PAT with contents:write + bypass on protected master) when GITHUB_TOKEN cannot push.
• Version Bump: workflow_dispatch only (removes failing push hooks on every merge); updates client.py UA; same PAT pattern; removed redundant publish.yml API dispatch (tag push triggers publish).

After merge (you)

If v2.5.7 still does not exist on GitHub, create it on the merge commit:

git checkout master && git pull
git tag -a v2.5.7 -m "Release 2.5.7"
git push origin v2.5.7

Add RELEASE_PUSH_TOKEN in repo Settings → Secrets if you want manual Auto Release / Version Bump workflows to push master without opening PRs.