fix: publish release bundle assets

[sven1103-agent]

Summary

• add a release workflow and packaging script that publishes the bundle tarball and matching SHA-256 checksums for each GitHub release
• align the checked-in bundle manifest with the current oc bundle contract by using semver manifest_version and release provenance fields
• update the README to point at the CLI-owned contract docs and document prerelease usage with explicit --version

Validation

• sh scripts/test-release-bundle
• sh scripts/release/build-bundle-release.sh --tag 1.0.0-alpha.1 --output-dir dist