FEL-623: restore automatic Maven publication

[codeyousef]

Summary

• restore automatic Maven Central publication after successful verification on pushes to main
• keep pull requests verification-only and retain workflow_dispatch as a main-branch fallback
• serialize release workflows and skip immutable Central upload/tag creation when the version tag already exists
• keep GitHub Release creation repairable on reruns and require the changelog version to match version.properties
• date the 0.6.0.0 changelog entry and align release-status documentation

Root cause

The identity-platform release hardening split verification and publication, but restricted the publish job to workflow_dispatch. That regressed the repository's established push-to-main publication behavior.

Verification

• npm run typecheck --prefix e2e-tests
• npm test --prefix e2e-tests
• parsed .github/workflows/publish.yml with PyYAML
• validated the first changelog version equals version.properties
• git diff --check

Linear: FEL-623