fix: align auth-disabled mode and mock history loading (#3471)

* fix: align auth-disabled mode and mock history loading

* fix: address auth-disabled review feedback

* test: cover auth-disabled backend contract

* style: format frontend tests

* fix: address follow-up review comments

frontend/tests/e2e-real-backend/auth-disabled-contract.spec.ts

@@ -0,0 +1,16 @@
+import { expect, test } from "@playwright/test";
+
+import { AUTH_DISABLED_USER } from "../../src/core/auth/auth-disabled-user";
+
+const APP = "http://localhost:3000";
+
+test.describe("auth-disabled contract (real backend)", () => {
+  test("gateway /auth/me returns the frontend synthetic user without a cookie", async ({
+    context,
+  }) => {
+    const resp = await context.request.get(`${APP}/api/v1/auth/me`);
+
+    expect(resp.status(), await resp.text()).toBe(200);
+    await expect(resp.json()).resolves.toEqual(AUTH_DISABLED_USER);
+  });
+});