test(agents): dedupe subagent registry test mocks

src/agents/subagent-registry.nested.test.ts

@@ -1,18 +1,5 @@
 import { afterEach, describe, expect, it, vi } from "vitest";
-
-const noop = () => {};
-
-vi.mock("../gateway/call.js", () => ({
-  callGateway: vi.fn(async () => ({
-    status: "ok",
-    startedAt: 111,
-    endedAt: 222,
-  })),
-}));
-
-vi.mock("../infra/agent-events.js", () => ({
-  onAgentEvent: vi.fn(() => noop),
-}));
+import "./subagent-registry.mocks.shared.js";
 
 vi.mock("../config/config.js", () => ({
   loadConfig: vi.fn(() => ({