Partial Prefetching optimizer

Optimize each requested source link and destination as its own contract. Turn the requested prefetched UI, navigation-only UI, and trigger into a production instant() test. Record the current behavior, make the smallest optimization, verify the differential, and keep the passing test as regression coverage.

Before making framework changes, read the bundled Optimizing prefetching guide at node_modules/next/dist/docs/01-app/02-guides/optimizing-prefetching.md. If the bundled guide is unavailable, use the online guide. It is the source of truth for prefetch stages, prefetch={true}, session-specific UI, and cost trade-offs.