fix(kit): avoid behavior change based on NODE_ENV

[pi0]

🔗 Linked issue

resolves nuxt/nuxt#13399

related #3693 (comment)

❓ 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

If NODE_ENV is set to anything other than development, nuxi dev will build for production! This issue was because we weren't setting dev override and nuxt falling back to std-env to detect it.

As to fix the root-cause, kit purely depends on C12 config types to avoid creating confusing interfaces that made this issue happen.

Options of loadNuxt changes (rootDir => cwd, config => overides) but preserved as backward compatibility.

📝 Checklist

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

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