fix(nuxi): update api template to h3 event format

[Diizzayy]

• 📖 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

This PR updates nuxi add api behavior to match the direction detailed in unjs/h3#73 and documented in #4174.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly. docs: add server routes documentation #4174

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[pi0]

Thanks!