chore: make changelog mandatory in PR skills

.agents/skills/PR_WORKFLOW.md

@@ -110,9 +110,9 @@ Before any substantive review or prep work, **always rebase the PR branch onto c
 - During `prepare-pr`, use this commit subject format: `fix: <summary> (openclaw#<PR>) thanks @<pr-author>`.
 - Group related changes; avoid bundling unrelated refactors.
 - Changelog workflow: keep the latest released version at the top (no `Unreleased`); after publishing, bump the version and start a new top section.
-- When working on a PR: add a changelog entry with the PR number and thank the contributor.
+- When working on a PR: add a changelog entry with the PR number and thank the contributor (mandatory in this workflow).
 - When working on an issue: reference the issue in the changelog entry.
-- Pure test additions/fixes generally do **not** need a changelog entry unless they alter user-facing behavior or the user asks for one.
+- In this workflow, changelog is always required even for internal/test-only changes.
 
 ## Gate policy
 
@@ -233,7 +233,7 @@ Go or no-go checklist before merge:
 
 - All BLOCKER and IMPORTANT findings are resolved.
 - Verification is meaningful and regression risk is acceptably low.
-- Docs and changelog are updated when required.
+- Changelog is updated (mandatory) and docs are updated when required.
 - Required CI checks are green and the branch is not behind `main`.
 
 Expected output:

.agents/skills/prepare-pr/SKILL.md

@@ -67,7 +67,7 @@ jq -r '.findings[] | select(.severity=="BLOCKER" or .severity=="IMPORTANT") | "-
 
 Fix all required findings. Keep scope tight.
 
-3. Update changelog/docs when required
+3. Update changelog/docs (changelog is mandatory in this workflow)
 
 ```sh
 jq -r '.changelog' .local/review.json

.agents/skills/review-pr/SKILL.md

@@ -123,7 +123,7 @@ Minimum JSON shape:
     "result": "pass"
   },
   "docs": "up_to_date|missing|not_applicable",
-  "changelog": "required|not_required"
+  "changelog": "required"
 }
 ```