fix(prerender): only try to add / after prerender:routes hook

[danielroe]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 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)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This is more a proposal for discussion - please feel free to close if you disagree.

As Nitro is becoming less opinionated, I think it might be good to avoid defaulting to prerendering the / route. It makes it difficult for frameworks to know whether this path has been explicitly added by a user or module hook, or whether this is a Nitro default.

I'm looking to resolve nuxt/nuxt#26694, and we can work around this for that PR but I think it would be simpler for a framework to add the list and not have to remove any defaults.

📝 Checklist

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