Add plugin system

plugins/analytics.js

@@ -0,0 +1,7 @@
+module.exports = {
+  onPageRendered: async ({ html, file }) => {
+    // Example: inject analytics script into each page
+    const snippet = '\n<script>console.log("Page viewed: ' + file + '")</script>';
+    return html.replace('</body>', `${snippet}</body>`);
+  }
+};