Support pre-release publishing in npm-publish workflow

[minggangw]

Add automatic dist-tag detection to the publish step. npm requires --tag when publishing pre-release versions to prevent them from becoming the default latest on the registry.

The new Determine dist-tag step reads the version from package.json and extracts the pre-release label (e.g. alpha, beta, rc) if present, otherwise defaults to latest. This tag is passed to npm publish --tag.

Examples:

• 1.9.0-alpha.0 → --tag alpha
• 1.9.0-beta.1 → --tag beta
• 1.9.0-rc.0 → --tag rc
• 1.9.0 → --tag latest

Fix: #1459