ci(whatsnew): generate release highlights via GitHub Models

Activate the What's New highlights step that condenses each release's
Features into <=8 short bullets and injects a <!-- whatsnew --> block the
app reads (utils/whatsNew.parseWhatsNew), with a deterministic fallback.

Runs as a needs: job inside the release-please workflows rather than on a
standalone release: published trigger, because release-please creates the
release with GITHUB_TOKEN and GitHub never starts new workflow runs from
token-generated events -- a standalone trigger would never fire. Shared as
a reusable workflow_call so the stable and beta channels stay in sync.

Best-effort: continue-on-error + fallback mean it can never break a release.
Requires GitHub Models enabled for the org; until then the fallback is used.

.github/workflows/release-please.yml

@@ -34,3 +34,16 @@ jobs:
           echo "" >> $GITHUB_STEP_SUMMARY
           echo "Docker images will be built and tagged with this version." >> $GITHUB_STEP_SUMMARY
 
+  # Best-effort "What's New" highlights on the freshly-created release. Runs in
+  # this same workflow run (not a `release:` trigger) because release-please
+  # creates the release with GITHUB_TOKEN, which never starts new workflow runs.
+  whatsnew:
+    needs: release-please
+    if: ${{ needs.release-please.outputs.release_created }}
+    permissions:
+      contents: write   # edit the release body
+      models: read       # GitHub Models (free tier)
+    uses: ./.github/workflows/whatsnew-highlights.yml
+    with:
+      tag: ${{ needs.release-please.outputs.tag_name }}
+