Add Packagist auto-update workflow

Author: Sterling

.github/workflows/update-packagist.yml

@@ -0,0 +1,17 @@
+name: Update Packagist
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Notify Packagist
+        if: ${{ vars.PACKAGIST_USERNAME != '' }}
+        run: |
+          curl -s -X POST "https://packagist.org/api/update-package?username=${{ vars.PACKAGIST_USERNAME }}&apiToken=${{ secrets.PACKAGIST_API_TOKEN }}" \
+            -d '{"repository":{"url":"https://github.com/hdresearch/php-sdk"}}' \
+            -H "Content-Type: application/json"
+          echo "✅ Packagist notified"