Make GitHub Release publishing idempotent

[Dezoff-max]

Root cause

The v0.3.0 workflow packaged successfully, then failed because gh release create was called after the same tag release had already been published.

Fix

• create the release only when it does not exist
• otherwise replace matching ZIP/checksum assets with gh release upload --clobber
• preserve the existing release title and English notes

Verification

• workflow YAML parse passed
• embedded publish shell passed bash -n
• stubbed missing-release branch selected gh release create
• exact existing-release branch refreshed v0.3.0 successfully
• clean downloaded SHA-256 verification passed
• release metadata and asset names remained correct