feat(ci): add changelog gate to PR checks [skip ci]

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.mokogitea/workflows/pr-check.yml

@@ -108,7 +108,8 @@ jobs:
       - name: Detect platform
         id: platform
         run: |
-          PLATFORM=$(cat .mokogitea/manifest.xml 2>/dev/null | tr -d '[:space:]')
+          # Parse manifest for platform detection
+          PLATFORM=$(php /tmp/mokostandards-api/cli/manifest_read.php --path . --field platform 2>/dev/null)
           [ -z "$PLATFORM" ] && PLATFORM="generic"
           echo "platform=$PLATFORM" >> "$GITHUB_OUTPUT"
 
@@ -192,3 +193,32 @@ jobs:
           FILE_COUNT=$(find "$SOURCE_DIR" -type f | wc -l)
           echo "Source: ${FILE_COUNT} files"
           [ "$FILE_COUNT" -gt 0 ] || { echo "::error::Source directory is empty"; exit 1; }
+
+  # ── Changelog Gate ────────────────────────────────────────────────────
+  changelog:
+    name: Changelog Updated
+    runs-on: ubuntu-latest
+    if: github.base_ref == 'main'
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Check CHANGELOG.md was updated
+        run: |
+          BASE="${{ github.event.pull_request.base.sha }}"
+          HEAD="${{ github.event.pull_request.head.sha }}"
+
+          if git diff --name-only "$BASE" "$HEAD" | grep -q "^CHANGELOG.md$"; then
+            echo "CHANGELOG.md updated"
+          else
+            # Allow [skip changelog] in PR title or body
+            PR_TITLE="${{ github.event.pull_request.title }}"
+            PR_BODY="${{ github.event.pull_request.body }}"
+            if echo "$PR_TITLE $PR_BODY" | grep -qi "\[skip changelog\]"; then
+              echo "::warning::Changelog skip requested via [skip changelog]"
+              exit 0
+            fi
+            echo "::error::CHANGELOG.md must be updated before merging to main. Add [skip changelog] to the PR title to bypass."
+            exit 1
+          fi