docs(changelog): note the validation framework rename

CHANGELOG.md

@@ -362,6 +362,21 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- The validation framework's public types are renamed to match the
+  OpenAPIKit validation idiom's canonical names: `Check` is now
+  `Validation`, `Issue` is `ValidationError`, `Issue.Collection` is the
+  top-level `ValidationErrorCollection` (with `.issues` renamed to
+  `.values`), `SubjectContext` is `ValidationContext`, `BuiltinCheck` is
+  `BuiltinValidation`, and `AnyCheck` is `AnyValidation`. `ValidationError.description`
+  drops its severity prefix and renders `"<reason> at root of document"` /
+  `"<reason> at path: <path>"`. `Validator` is now a reference-type
+  `final class` with a two-tier `nonReferenceDefaultValidations`/
+  `referenceDefaultValidations` split, generic over both the walked
+  `Subject` type and the cross-cutting `Document` via a new `Traversable`
+  protocol; `Tagged.Validator` is now a type alias over the same shared
+  class instead of its own duplicated traversal implementation. The JSON
+  representability rule set (`PureYAMLJSON`) is built with the same tiered
+  constructor. Adds the `unwrap` combinator.
 - `parseTagged(_:)`/`parseTaggedStream(_:)` now preserve alias references
   as `alias` nodes instead of expanding them into copies of the anchored
   node, and populate the new `anchor`/`style` fields from the source.