fix production prerender without auth config

lib/auth/server.ts

@@ -26,6 +26,12 @@ function required(name: string): string {
   return value;
 }
 
+function hasAuthConfiguration(): boolean {
+  return ["DATABASE_URL", "BETTER_AUTH_URL", "BETTER_AUTH_SECRET", "ADMIN_EMAIL"].every(
+    (name) => Boolean(process.env[name]),
+  );
+}
+
 function createAuth() {
   const adminEmail = required("ADMIN_EMAIL");
 
@@ -109,6 +115,11 @@ export async function getAdminSession(): Promise<AdminSession | null> {
     };
   }
 
+  // Public pages can be prerendered without the runtime auth secret. In that
+  // case the header simply omits the admin link; auth routes still fail loudly
+  // through getAuth() when authentication is actually used.
+  if (!hasAuthConfiguration()) return null;
+
   const session = await getAuth().api.getSession({ headers: await headers() });
   if (
     !session?.session ||