Fix Codex Responses API base URL

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/gateway/gateway_test.go

@@ -331,7 +331,7 @@ func TestApplyAndRestoreCodex(t *testing.T) {
 		t.Fatalf("injection = %v", out["injection"])
 	}
 	table := injection["table"].(map[string]any)
-	if table["wire_api"] != "responses" || table["base_url"] != "http://127.0.0.1:18787" {
+	if table["wire_api"] != "responses" || table["base_url"] != "http://127.0.0.1:18787/v1" {
 		t.Errorf("injected table = %v", table)
 	}
 	if table["experimental_bearer_token"] != env.store.Config().RelayToken {