fix(frontend): declare admin users runtime locally

frontend/src/app/api/admin/users/route.ts

@@ -1 +1,3 @@
-export { DELETE, GET, PATCH, POST, PUT, runtime } from "../customers/route";
+export const runtime = "nodejs";
+
+export { DELETE, GET, PATCH, POST, PUT } from "../customers/route";

frontend/tests/admin-users-contract.test.ts

@@ -39,5 +39,7 @@ test("admin_users migration is service-role-only and auditable", () => {
 });
 
 test("legacy admin users route aliases the guarded customer resource", () => {
-  assert.match(usersSource, /export \{ DELETE, GET, PATCH, POST, PUT, runtime \} from "\.\.\/customers\/route"/);
+  assert.match(usersSource, /export const runtime = "nodejs"/);
+  assert.match(usersSource, /export \{ DELETE, GET, PATCH, POST, PUT \} from "\.\.\/customers\/route"/);
+  assert.doesNotMatch(usersSource, /export \{[^}]*\bruntime\b[^}]*\} from/);
 });