build: enforce changelog workflow in CI

changes/README.md

@@ -0,0 +1,21 @@
+# Changelog Fragments
+
+Add one `.md` file per user-visible PR in this directory.
+
+Use this format:
+
+```md
+type: added
+area: overlay
+
+- Added keyboard navigation for Yomitan popups.
+- Added auto-pause toggle when opening the popup.
+```
+
+Rules:
+
+- `type` required: `added`, `changed`, `fixed`, `docs`, or `internal`
+- `area` required: short product area like `overlay`, `launcher`, `release`
+- each non-empty body line becomes a bullet
+- `README.md` is ignored by the generator
+- if a PR should not produce release notes, apply the `skip-changelog` label instead of adding a fragment