Adopt PromptKit v0.15.0 in ckprompt

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # PromptKit request validation implementation plan
 
-Status: ready for implementation; no implementation stages have been completed.
+Status: Stage 1 complete; implementation is ongoing.
 
 ## Authority, scope, and baseline
 
@@ -11,8 +11,8 @@ user choices. The [architecture policy](../policy/architecture.md), accepted
 [ADRs](../adr/), and existing public contracts remain authoritative.
 
 The planning baseline is commit `1119bda6b720171c708f3e6d03c5c8690b65ea81`.
-The implementation still requires PromptKit v0.14.0; the accepted roadmap adds
-v0.15.0 adoption and `promptkit requirements validate PROMPT_ID`.
+The implementation now selects released PromptKit v0.15.0; the accepted roadmap
+adds `promptkit requirements validate PROMPT_ID`.
 
 The deliverable is the complete accepted feature, including the independently
 optional callback, suite-returning helper, nil-builder path, file bindings,
@@ -85,6 +85,14 @@ in Stage 9 if required. Prose and attribution checks follow
 **Complete when:** ckprompt selects released PromptKit v0.15.0, its current
 suite passes, notices identify that release, and module boundaries are unchanged.
 
+**Completed:** 2026-10-12. Updated ckprompt to released PromptKit v0.15.0 and
+refreshed its integration attribution at commit
+`635674c066d0b432187f96e72b9c03d085443ac5`. `GOTOOLCHAIN=local go test
+-count=1 ./...` passed from `integrations/ckprompt`; `go list -m` selected v0.15.0.
+The released source contains `Engine.ValidateRequest`; PromptKit's LICENSE and
+COPYRIGHT are unchanged from v0.14.0. The dependency graph, other versions, and
+checked-in replacement metadata are unchanged.
+
 ## Stage 2: Add the public capability and bundled validation adapter
 
 **Primary files:** `integrations/ckprompt/adapters.go`, a new owning-package