v1.5.0-alpha.1: refactor: use git tags instead of commit messages for releases

- Changed from unreliable commit message parsing to git tag detection
- Only runs publish on tag pushes (refs/tags/*)
- Detects alpha/beta/rc from tag names (v1.5.0-alpha.1)
- More reliable and follows standard release practices

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Co-Authored-By: Claude <noreply@anthropic.com>