fix(vite): unset build.watch options for production build

[pi0]

🔗 Linked issue

Resolvesnuxt/nuxt#14320

❓ 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

A regression was introduced in rc.5 with #5632 by adding build.watch key. The change likely only unrevealed an issue in vite. When this key exists for production, the server build promise succeeds but no output is generated! Removing watch key from production seems to solve this issue. This PR also refactors config placement to the shared one for more readability.

📝 Checklist

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

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[pi0]

We likely need to investigate it sometime later or add an output checker for server.mjs. Vite failed build was completely silent!