Add Lookbook preview for lazy-loaded tab panels

[joshsadam]

What does this PR do and why?

Adds a new Lookbook preview that demonstrates lazy-loaded tab panels using Pathogen::Tabs#with_lazy_panel and Turbo Frames.

The preview shows a three-tab layout where the selected panel renders immediately and the other panels fetch mocked Turbo Frame responses when their tabs become visible. To support this without adding demo-only Rails routes, the Lookbook preview layout now boots MSW (Mock Service Worker) before Turbo starts. MSW intercepts requests to /lookbook-mocks/tabs/lazy-load/:panel and returns realistic frame HTML with a short artificial delay.

Changes include:

• New Turbo Frame Lazy Load preview under Pathogen::Tabs
• lookbook_mocks/tabs_lazy_load.js MSW handlers and lookbook_preview.js entry point
• mockServiceWorker.js in demo/public/ for browser interception
• MSW added as a dev dependency (package.json, pnpm-lock.yaml)
• ESLint config updated to allow MSW imports in demo JavaScript
• Minor copy updates in the Advanced Features preview

Screenshots or screen recordings

Requests:

How to set up and validate locally

1. Update dependencies in root folder bin/setup
2. cd demo & bin/dev
3. Open http://localhost:3001/lookbook
4. Navigate to Pathogen::Tabs → Turbo Frame Lazy Load
5. Confirm the Summary tab content is visible on load
6. Click Metrics and Timeline — each panel should show a brief loading state, then render mocked content with a green Loaded by MSW badge
7. Optionally review Advanced Features for updated lazy-loading documentation copy

PR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the PR acceptance checklist for this PR.