fix(nuxt): allow island renders without / route

[danielroe]

🔗 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)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Previously we were throwing a 404 if the root ~/pages/index.vue path didn't exist - server components would silently fail to render. 😬

📝 Checklist

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

[huang-julien]

indeed 😮 thanks 🙌 !