Suspense fallback flashes on cached navigations

The brief

Hydrogen flashes the suspense fallback on back-navigations even when the route payload is fully cached. Cached routes should restore instantly with no flash.

Acceptance criteria

• Back/forward over cached routes renders with zero fallback frames
• Stale-while-revalidate still refreshes in the background
• No regression in existing streaming SSR tests
• E2E test covering cached navigation included