Disable Jetpack Stats for local sites

[shaunandrews]

Related issues

• Related to https://linear.app/a8c/issue/STU-1945/investigate-localhost-traffic-inflating-wordpresscomjetpack-stats

How AI was used in this PR

Codex investigated the localhost Stats repro, confirmed that local Studio-rendered pages can emit Jetpack Stats pixels with live blog IDs, and prepared this scoped fix. I reviewed the generated change and kept the PR limited to the Studio MU plugin behavior plus a regression test.

Proposed Changes

• Prevent Studio-served local sites from reporting page views to the remote WordPress.com/Jetpack Stats site when an imported or synced local database still contains a live Jetpack connection.
• Preserve the existing local-development behavior that disables Jetpack Protect for auto-login, while also disabling Jetpack Stats through the same module filter path.
• Keep the fix server-side in the local WordPress runtime so it applies to Studio previews, thumbnail captures, and local sites opened in an external browser.

Testing Instructions

• npx eslint --fix tools/common/lib/mu-plugins.ts tools/common/lib/tests/mu-plugins.test.ts
• npm test -- tools/common/lib/tests/mu-plugins.test.ts
• npm run typecheck

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?