Add initial project files

apps/web/web-runtime/lib/site-url.ts

@@ -0,0 +1,18 @@
+/**
+ * The public origin of this site, used as Next's `metadataBase`.
+ */
+const DEVELOPMENT_FALLBACK = 'http://localhost:3000';
+
+export function siteUrl(): URL {
+  const configured = process.env['SITE_URL']?.trim();
+
+  if (configured) {
+    return new URL(configured);
+  }
+
+  if (process.env.NODE_ENV === 'production') {
+    console.error('SITE_URL is not set — canonical and Open Graph URLs will point at localhost.');
+  }
+
+  return new URL(DEVELOPMENT_FALLBACK);
+}