Cache Components: align short-lifetime cache behavior with partial prefetching

## Next.js Change

**Commits:**
- [`e974969`](https://github.com/vercel/next.js/commit/e974969ddd0d4dfe1529ae8ad1159a6f91ef1327) ([#98339](https://github.com/vercel/next.js/pull/98339))
- [`f4449e8`](https://github.com/vercel/next.js/commit/f4449e8fa58d137a82bb3667eedfff80466de3ae) ([#98342](https://github.com/vercel/next.js/pull/98342))
- [`b0b7a42`](https://github.com/vercel/next.js/commit/b0b7a429b931b08eb33b18f5c31caf25864004b0) ([#98278](https://github.com/vercel/next.js/pull/98278))

## What changed

Next.js refined Cache Components behavior when `cacheLife()` has short `stale` or `expire` values:

- `stale < MIN_SHELL_STALE` means a cache is excluded from App Shells but remains eligible for a per-link prefetch. This is prefetch-only data, not runtime data.
- `stale < MIN_PREFETCHABLE_STALE` excludes a cache from all prerenders and prefetches.
- `expire < MIN_PRERENDERABLE_EXPIRE` excludes a cache from static prerenders but permits it in runtime prerenders.
- `unstable_prefetch()` and prefetch-only short-stale caches must not be treated as runtime-data access.
- Instant Validation must apply these rules on both cold and warm caches during development and build-time validation.
- When a revalidated route starts accessing request data, the client segment cache must issue the required runtime follow-up rather than reuse incomplete static content.

## Impact on vinext

vinext implements the Cache Components / `'use cache'` surface and App Router navigation. Its cache metadata and prefetch behavior should not classify prefetch-only cached content as runtime data or serve incomplete cached content after a route changes its dynamic requirements.

## Acceptance criteria

- [ ] Preserve `stale` when reading and writing cache entries.
- [ ] Implement the three upstream cache eligibility boundaries for any supported partial-prefetch/App Shell mode.
- [ ] Ensure `unstable_prefetch()` and shell-excluded short-stale caches do not trigger runtime-data handling.
- [ ] Validate the behavior consistently for cache misses and hits in development and production builds.
- [ ] Ensure a static-to-dynamic revalidation triggers a runtime follow-up before navigation consumes incomplete cached content.
- [ ] Add focused regression coverage for each boundary and the static-to-dynamic revalidation path.

## References

- https://github.com/vercel/next.js/commit/e974969ddd0d4dfe1529ae8ad1159a6f91ef1327
- https://github.com/vercel/next.js/commit/f4449e8fa58d137a82bb3667eedfff80466de3ae
- https://github.com/vercel/next.js/commit/b0b7a429b931b08eb33b18f5c31caf25864004b0

Start by comparing vinext's Cache Components, 'use cache', and App Router prefetch behavior with upstream commits e974969, f4449e8, and b0b7a42. Trace cache metadata through reads and writes and cold/warm validation, then add focused regression coverage for the three boundaries and static-to-dynamic revalidation; done means the acceptance criteria pass in development and production builds.

Written by the indexing model from the issue text.