fix: make oxlint an optional peer dependency to avoid pnpm vitest duplication

[NisargIO]

Summary

This PR addresses the issue where installing react-doctor as a workspace devDependency in pnpm monorepos using vite-plus/vitest causes duplicate Vitest module instances.

Root Cause

When react-doctor is installed, its dependency on oxlint introduces a different peer-dependency fingerprint. pnpm creates multiple physical installations of the same Vitest fork when peer contexts differ, causing Vitest's hook registry to split between instances. This results in:

Error: Vitest failed to find the current suite.

Changes

1. Move oxlint to optional peer dependency (peerDependencies with peerDependenciesMeta.optional: true) in both @react-doctor/core and react-doctor

   • This allows pnpm to use a single shared oxlint instance when users install it separately
   • Users who don't have oxlint installed will get a helpful error message

2. Add OxlintNotInstalledError with clear installation instructions:

   oxlint is not installed. Install it as a dependency:
   
     npm install -D oxlint
     # or: pnpm add -D oxlint
     # or: yarn add -D oxlint
   
   In pnpm monorepos using vite-plus/vitest, install oxlint at the workspace root 
   to avoid duplicate module instances.
   

3. Add troubleshooting documentation in README with workarounds:

   • Use pnpm dlx react-doctor@latest (recommended for monorepos)
   • Install oxlint at workspace root separately
   • Use pnpm overrides to force single vitest instance

Testing

• All existing tests pass
• TypeScript typecheck passes
• Verified error message renders correctly when oxlint is not installed

Migration for Users

Users who install react-doctor will now need to also install oxlint:

npm install -D react-doctor oxlint
# or: pnpm add -D react-doctor oxlint

For users running via npx/pnpm dlx, no changes are needed as the temporary installation handles dependencies.

  

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/eslint-plugin-react-doctor@701

npm i https://pkg.pr.new/oxlint-plugin-react-doctor@701

npm i https://pkg.pr.new/react-doctor@701

commit: 93f563e

[github-actions]

No React Doctor issues found. 🎉

_{Reviewed by React Doctor for commit 93f563e.}