chore: add CHANGELOG.md check workflow on PRs

Fails a PR when CHANGELOG.md is not updated unless the description
states "No customer facing changes" to justify skipping the changelog.
Also documents the opt-out phrase in the PR template.

Author: joaodordio

.github/pull_request_template.md

@@ -9,6 +9,9 @@
 ## 🧪 How to test?
 > How to test the changes added?
 
+## 🧾 Changelog
+> Add an entry to `CHANGELOG.md`. If this PR has no customer facing changes, write "No customer facing changes" here to skip the changelog check.
+
 ## 📹 Loom recording if applicable
 > If it helps the reviewer, add a short Loom going over the changes or showcasing the change in behavior.
 

.github/workflows/changelog-check.yml

@@ -0,0 +1,42 @@
+name: Changelog Check
+on:
+  pull_request:
+    types: [opened, edited, synchronize, reopened]
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+  changelog:
+    name: Verify CHANGELOG update
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check CHANGELOG.md update or opt-out
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const optOut = 'No customer facing changes';
+            const body = context.payload.pull_request.body || '';
+
+            if (body.toLowerCase().includes(optOut.toLowerCase())) {
+              core.info(`PR description contains "${optOut}", skipping CHANGELOG.md check.`);
+              return;
+            }
+
+            const files = await github.paginate(github.rest.pulls.listFiles, {
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: context.payload.pull_request.number,
+              per_page: 100,
+            });
+
+            const changed = files.some((f) => f.filename === 'CHANGELOG.md');
+            if (changed) {
+              core.info('CHANGELOG.md was updated.');
+              return;
+            }
+
+            core.setFailed(
+              'CHANGELOG.md was not updated. Add a CHANGELOG.md entry, or if this PR has no customer facing changes, add "No customer facing changes" to the PR description to justify skipping the changelog.'
+            );