feat(create-rspack): add preview script and remove cross-env

[chenjiahan]

Summary

• Add rspack preview command to all Rspack templates.
• Remove the cross-env dependency, as Rspack CLI will set the process.env.NODE_ENV by default, see feat(cli): rspack preview support for nodeEnv flag and default env #9543

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for rspack canceled.

Name	Link
🔨 Latest commit	7f105ec
🔍 Latest deploy log	https://app.netlify.com/sites/rspack/deploys/67c6df7dd622c50008d20a58

[codspeed-hq]

CodSpeed Performance Report

Merging #9544 will not alter performance

_{Comparing create_rspack_preview_0304 (7f105ec) with main (fcb9339)}

Summary

✅ 7 untouched benchmarks