Add internal engine relocation candidate

docs/internal/overview.md

@@ -3,6 +3,10 @@
 ConfigKit exposes the root `configkit` package and keeps its document and YAML
 representations private. The implemented components and their owners are:
 
+- a temporary `internal/engine` relocation candidate containing a mechanical
+  copy of the root loading, decoding, resolution, provenance, inspection, and
+  rendering mechanisms with their behavior tests; it imports no root code and
+  is not yet used by the root package or consumers;
 - immutable semantic `Path` construction and strict JSON Pointer parsing;
 - detached effective presence/origin and chronological history queries in
   `metadata.go`, with provenance and diagnostic record types;