feat: automate tagging & publishing of release‑candidate builds

[Amnah199]

Background After we bump the version for release, we need to wait for the branch CI to go green, then create and push the annotated tag from VERSION.txt (v2.3.0‑rc1). Pushing the tag triggers Docker images, PyPI publication, and the GitHub Release page. These commands and the “wait‑for‑CI” step are manual.

Proposal Add a GitHub Actions workflow that, when triggered, ensures the release branch CI is green, creates the annotated tag, pushes it, and therefore starts the downstream build/publish jobs.

Criteria

• [ ] A new workflow file .github/workflows/tag-rc-release.yml.
• [ ] The first job calls GitHub Checks for the release branch and exits non‑zero if any required status is failing or in progress.
• [ ] When CI is all green, the workflow creates an annotated tag from VERSION.txt (git tag -m "" ) and pushes it with the GitHub token.
• [ ] The workflow prints a link to the new GitHub Release page (or the tag URL) on success.
• [ ] If the tag already exists, the workflow exits gracefully with a notice.
• [ ] Documentation (Notion) is updated to reference the new automated tagging workflow.