[docs] Clarify changelog workflow permissions (#118)

[coisa]

Summary

Documents the GitHub Actions repository settings required for the changelog release workflow introduced by #28.

Included

• explain that the changelog release flow is two-step:
  • workflow_dispatch prepares a release/v... pull request
  • merging that release pull request publishes the GitHub release and tag
• clarify that ordinary feature or fix pull requests merged into main do not publish releases
• document the required repository settings under Settings -> Actions -> General
• call out the blocked or grayed-out settings case and explain that it usually comes from repository permissions or organization policy, not branch protection
• update README and Sphinx docs where the release workflow is described

Validation

• git diff --check
• reviewed the updated docs in:
  • README.md
  • docs/usage/github-actions.rst
  • docs/internals/release-publishing.rst
  • docs/configuration/repository-setup.rst

Notes

This is a documentation follow-up to the changelog automation shipped in #28. It does not change the release strategy itself.

Closes #118
Related to #28

[github-actions]

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