chore: Fix types in tests 38/N.

src/gateway/server-methods/usage.test.ts

@@ -1,4 +1,5 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { OpenClawConfig } from "../../config/config.js";
 
 vi.mock("../../infra/session-cost-usage.js", async () => {
   const actual = await vi.importActual<typeof import("../../infra/session-cost-usage.js")>(
@@ -63,7 +64,7 @@ describe("gateway usage helpers", () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date("2026-02-05T00:00:00.000Z"));
 
-    const config = {} as unknown as ReturnType<import("../../config/config.js").loadConfig>;
+    const config = {} as OpenClawConfig;
     const a = await __test.loadCostUsageSummaryCached({
       startMs: 1,
       endMs: 2,