fix(build): do not override publicAssets in build

[antfu]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

There is a misalignment across dev and build. In dev, the middleware is registered in the normal order, which mean eailer items in publicAssets will have higher priority. While in build, fes.copy defaults to overrides the existing files, making the priority in the oppsite direction.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.