2.3.1 release review notes

This patch packages the updated numerical-library comparison and release metadata. It does not change Pascal implementation units, numerical behavior, public declarations, or runtime dependencies. The versioned API snapshot and reference identify the 2.3.1 release while preserving the 2.3.0 API surface.

The supported target matrix and runtime qualification carry forward from 2.3.0. Documentation, package metadata, repository CI, and the release branch's clean-archive qualification are checked as part of this release. The documentation workflow now rebuilds v2.3.0 alongside the other archived site versions. The release-specific numerical-evidence catalogue carries forward from 2.3.0 and records that source release.