fix(release): merge release commits through PRs

[rozsazoltan]

Summary

Routes automated release metadata changes through a release branch and pull request instead of pushing directly to master.

• Adds pull-requests: write permission to the release workflow.
• Pushes the chore/release-vX.Y.Z branch.
• Creates and squash-merges a pull request through the GitHub API.
• Resolves the merged master SHA before tagging and publishing the release.
• Removes the temporary release branch after merging.

Why

master requires pull requests. The previous workflow attempted a direct push and was rejected with GH013.

Validation

• YAML syntax validation.
• bash -n validation of the updated release preparation step.
• git diff --check.