Backfill GitHub releases for published PyPI versions

[zeevdr]

Description

PyPI has published alpha versions but GitHub Releases is empty. Visitors landing on the repo see 'no releases' → assume project is dead. Directly hurts credibility + discovery.

Acceptance criteria

• List all published PyPI versions
• For each existing tag: create GitHub release with --generate-notes
• Attach wheel + sdist as release artifacts (download from PyPI)
• Update release workflow to emit GH release on tag push going forward