perf(CLI): change default config loader from jiti to auto

[chenjiahan]

Summary

Update the default config loader to 'auto' which first attempts to use Node.js native loader before falling back to jiti. This provides better performance when native TypeScript support is available while maintaining compatibility.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for rsbuild ready!

Name	Link
🔨 Latest commit	d8a58c3
🔍 Latest deploy log	https://app.netlify.com/projects/rsbuild/deploys/68f8a65d1de4bb000875850d
😎 Deploy Preview	https://deploy-preview-6406--rsbuild.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 56 (🔴 down 11 from production) Accessibility: 97 (no change from production) Best Practices: 100 (no change from production) SEO: 100 (no change from production) PWA: 60 (no change from production) View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[Copilot]

Pull Request Overview

This PR updates the default config loader from jiti to auto for improved performance. The auto loader attempts to use Node.js native TypeScript support first before falling back to jiti, providing better performance when native support is available while maintaining backward compatibility.

Key Changes:

• Changed the default CLI --config-loader option from 'jiti' to 'auto'
• Updated documentation to reflect auto as the default loader
• Refactored config loading logic to wrap jiti fallback in proper conditional check

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/core/src/cli/commands.ts	Changed default config loader from 'jiti' to 'auto'
packages/core/src/loadConfig.ts	Refactored jiti fallback logic and added Boolean wrapper for useNative flag
website/docs/en/guide/configuration/rsbuild.mdx	Updated English documentation to list 'auto' as default loader
website/docs/zh/guide/configuration/rsbuild.mdx	Updated Chinese documentation to list 'auto' as default loader

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}