docs: changelog for 4.2.0

Promotes the accumulated [Unreleased] section to 4.2.0.

Minor rather than patch: templates/site-check is new public API for every consumer of this catalog, and the shared preset gained the path-based evidence freeze.

Contents of 4.2.0:

Added — site-check component, ADOPTION.md, inherited Renovate enrollment, RENOVATE_FORCE cadence normalizer, validate:renovate-config job, needs: [] on the renovate job.

Changed — path-based evidence freeze, TypeScript ceilinged below v7, scan timeout raised to 3h, autodiscovery skips purge-pending projects, runner preset documents cadence + enrollment doctrines.

Fixed — glab looked up on the right forge, scheduled runs actually open merge requests, UBI grouping covers UBI10, catalog component pins no longer emit a spurious lookup-failure warning (closes #2 (closed)).

Tag v4.2.0 follows once this lands, annotated and signed per CONTRIBUTING's tag protocol.