Test: Pre-registered Handler

What this tests:

The preRegisteredHandler prop on BackNavigationHandlerProvider.

How it works:

• preRegisteredHandler runs FIRST with highest priority
• If it returns false → Navigation blocked, other handlers skip
• If it returns true → Regular handlers run next

Expected behavior on this page:

• Back → "Regular Handler" dialog appears
• (This means preRegisteredHandler returned true)

Use case:

Close global modals/overlays before page handlers run. See _app.tsx for implementation.