docs: soften troubleshooting claims around vite config loading

[FleetAdmiralJakob]

Coming from #930 and oxc-project/oxc#21057 since I heard documentation improvements are welcomed in this project.

Motivation

• Clarify current limitations when vp lint, vp fmt, and the Oxc VS Code extension read vite.config.ts so users understand why lint/format integrations can fail.
• Provide concrete supported patterns and common failure modes to reduce confusion around functional/async and transform-dependent configs.
• Offer practical workarounds (like the one I mentioned here: vp lint/fmt + IDE: Known vite.config.ts releated issues #930 (comment)) and a note about VS Code multi-root workspace behavior that has caused incorrect workspace resolution.

Description

• Added a new section explaining that vp lint, vp fmt, and the Oxc VS Code extension read the lint/fmt blocks from vite.config.ts and have limitations.
• Documented currently supported static exports such as export default { ... } and export default defineConfig({ ... }).
• Documented failure cases including defineConfig with functional or async factories and configs relying on Vite bundling/transform behavior, with a link to the related issue for more context.
• Added recommended workarounds and a VS Code multi-root workspace note to help users mitigate the observed integration issues.

Testing

• No automated tests were added or modified for this documentation-only change.

[netlify]

✅ Deploy Preview for viteplus-preview canceled.

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[FleetAdmiralJakob]

Deployment preview looks good to me

[leaysgur]

In the short term, it might be more convenient to look it up in the docs rather than searching GitHub issues.
However, I do think this is more of a bug and should be resolved as soon as possible. (We apologize for the inconvenience though)

Regarding the presentation, would you mind if I left the decision up to @cpojer ?