refactor(nuxt): use pathe.join for layer lookup

[TheAlexLichter]

🔗 Linked issue

Follow-up of #9521

❓ Type of change

• ♻️ Refactor
• 📖 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

Use pathe.join for app components too

📝 Checklist

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

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[vercel]

@manniL is attempting to deploy a commit to the Nuxt Team on Vercel.

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[pi0]

Thanks!