Index: src/routes/og.js
===================================================================
--- src/routes/og.js	(revision 69815b232bc91b7504ea8b28d3e2f66949f216ed)
+++ src/routes/og.js	(revision 69815b232bc91b7504ea8b28d3e2f66949f216ed)
@@ -0,0 +1,29 @@
+/**
+ * GET /og/:slug.png — themed Open Graph card for a site (1200x630 PNG).
+ * Generated from the site's palette + accent (see OgImageService), cached.
+ * Used as the default og:image so every site has a branded social preview.
+ */
+import express from 'express';
+import db from '../config/database.js';
+import { ogImageFor } from '../services/OgImageService.js';
+
+const router = express.Router();
+
+router.get('/:slug.png', (req, res) => {
+  let site;
+  try {
+    site = db.prepare(
+      'SELECT slug, title, tagline, description, palette, accent FROM sites WHERE slug = ?'
+    ).get(req.params.slug);
+  } catch { /* db error → 404 below */ }
+  if (!site) return res.status(404).end();
+
+  const png = ogImageFor(site);
+  if (!png) return res.status(404).end(); // resvg unavailable → no card (graceful)
+
+  res.set('Content-Type', 'image/png');
+  res.set('Cache-Control', 'public, max-age=86400');
+  return res.send(png);
+});
+
+export default router;