ci: trigger publish on GitHub Release, drop version bump

[Vombato]

Summary

• Publish workflow triggers on release: published instead of workflow_dispatch.
• Releaser bumps package.json via PR, then creates a GitHub Release with a vX.Y.Z tag.
• Workflow derives version + dist-tag from the release and publishes via OIDC.
• Removes version bump, direct push to main, and the GitHub Release creation step.

Test plan

• Create a draft GitHub Release with tag vX.Y.Z (prerelease: optional).
• Publish the release and confirm the workflow runs and publishes to npm.