ci: prevent v2 release sync to main

[rmi22186]

Summary

• Remove the unused legacy .github/workflows/release.yml workflow.
• Update staging release Step 3 labels to describe v2 branch synchronization.
• Stop Step 3 from pushing v2 release commits to main; it now syncs development, master, and release-order branches only.

Context

main is now the v3 release line, while master remains v2. The v2 release process should not push release commits into v3, because main will be maintained independently with its own CI/CD.

Verification

• git diff --check
• Ruby YAML parse of .github/workflows/staging-step-3.yml
• Confirmed no remaining git push origin HEAD:main in .github/workflows

[cursor]

PR Summary

Medium Risk
Changes GitHub Actions release/synchronization behavior; misconfiguration could cause v2 release commits to be pushed to the wrong branches or fail to sync expected branches.

Overview
Removes the legacy .github/workflows/release.yml workflow.

Updates staging-step-3.yml to explicitly synchronize v2 release commits only to development, master, and the release-order-* branches, and no longer pushes to main (with updated job/workflow labeling and a clarifying comment about master being v2).

^{Reviewed by Cursor Bugbot for commit cc9eb80. Bugbot is set up for automated code reviews on this repo. Configure here.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud