fix: use route cache revalidation

[tomatotomata]

Summary

• use cacheControl.revalidate for APP_ROUTE cache entries
• add focused regression coverage for route entries, existing app pages, and fallback behavior

This fixes route handlers falling back to the default stale age when Next.js provides the route-level value through cacheControl.

Validation

• git diff --check
• Added Jest coverage in resolveRevalidateValue.test.ts

The package dependencies are not installed in this sparse checkout. The package Jest command timed out while the pnpm runtime attempted workspace dependency resolution, so I could not claim a local test pass. The upstream checks should run the full package suite.

The implementation was prepared with AI assistance and reviewed by me. I am responsible for the changes and this submission.

Closes #224

[AyronK]

This also addresses #231 right?

[tomatotomata]

I checked #231 against the current branch. This PR fixes the shared resolveRevalidateValue() path, so APP_ROUTE no longer falls back to the long default revalidation window. It does not change the separate tag derivation in set(), so it does not by itself fix revalidatePath() matching empty tags. I kept that second behavior out of this PR to stay aligned with #224; if you want the two fixes combined, I can extend the scope.