fix(payment): expose provider type for named gateways

packages/payment/test/runtime-api.test.ts

@@ -27,6 +27,7 @@ test("package APIs use server subjects and never expose gateway secrets", async
   const providerBody = await providers.text();
   expect(providers.status).toBe(200);
   expect(providerBody).toContain("testGateway");
+  expect(providerBody).toContain('"provider":"sandbox"');
   expect(providerBody).not.toContain("server-only");
 
   const denied = await POST({