skill(cc-adoption): add dev-only validation sweep reference (#96057)
### What?
Add an optional post-adoption reference to the Cache Components adoption
skill, `references/dev-only-validations.md`, and point to it from the
skill's further reading.
### Why?
After adoption the build passes, but dev validation (default
`validationLevel: 'warning'`) still raises instant-navigation insights
on every page load that never fail the build. The skill had no recipe
for sweeping them, so this closes that gap as a recommended next step,
offered as the smaller path to instant navigation for users who don't
want to adopt Partial Prefetching.
### How?
The reference details the loop: reuse the `next-dev-loop` preflight,
load each route in `next dev`, read the Insights tab and dev log, and
fix. The mechanics mirror the tested `next-partial-prefetching-adoption`
skill (dev log record, amber Insights tab, `get_errors` not
`get_request_insights`, webpack fallback). The further-reading section
now recommends the sweep and drops the standalone Prefetching bullet,
which the Partial Prefetching adoption skill already carries.