feat: replace semantic-release with explicit release workflow

[MehmetSecgin]

Summary

• remove semantic-release and replace it with one explicit GitHub Actions release flow
• derive release level from PR labels and compute the next version from the latest v* tag
• keep a dev version in git and stamp the publish version only on the CI runner

Breaking change

• the repo no longer treats committed package.json as the next release version source of truth
• releases now expect merged PRs on main and optional release:* labels

Validation

• npm run check
• npm test
• npm run build