feat: publish versioned image tag

[amandazhuyilan]

Pull Request

Summary

Publish a versioned release image when a release-please PR is merged, similar to what we have done in the aai-backend

Changes

• Add publish-release-image job to release-please.yml, gated on release_created == 'true'
• Builds and pushes sbp-backend:vX.Y.Z to the shared ECR repo at the release tag
• Reuses the existing staging deploy role — no new IAM changes
• No impact on build-push-deploy.yml or current dev/staging flows
• Note: PR #134 ("release 0.1.0") is open — merging it after this lands will trigger the first real push

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added or updated documentation where necessary
• I have run linting and unit tests locally
• The code follows the project's style guidelines

[marius-mather]

Can we make sure all actions are using their latest versions so they don't go out of date? Otherwise looks fine

[marius-mather]

good to go!