test(core-ui): add axe-core a11y assertions to CookieConsentBanner

Previous attempt was rejected because the axe-core a11y requirement
had no test infrastructure — ARIA roles were correct but unverified by
a scanner. This adds jest-axe (approved via library-decision trace) and
asserts toHaveNoViolations() for both modal and banner variants.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-ui/package.json

@@ -27,9 +27,11 @@
     "@testing-library/jest-dom": "^6.5.0",
     "@testing-library/react": "^16.0.0",
     "@testing-library/user-event": "^14.5.0",
+    "@types/jest-axe": "^3.5.9",
     "@types/react": "^19.0.0",
-    "jsdom": "^25.0.0",
     "@vitest/coverage-v8": "^3.0.0",
+    "jest-axe": "^10.0.0",
+    "jsdom": "^25.0.0",
     "vitest": "^3.0.0"
   }
 }

packages/core-ui/src/cookie-consent-banner/cookie-consent-banner.test.tsx

@@ -1,4 +1,5 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
+import { axe, toHaveNoViolations } from "jest-axe";
 import { renderWithProviders } from "@repo/core-testing/react";
 import { screen, fireEvent, waitFor } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
@@ -14,6 +15,8 @@ import {
 } from "./cookie-helpers";
 import type { ConsentCookieState } from "./types";
 
+expect.extend(toHaveNoViolations);
+
 beforeEach(() => {
   // Clear the consent cookie before each test
   document.cookie = `${CONSENT_COOKIE_NAME}=; Max-Age=0; Path=/`;
@@ -452,3 +455,24 @@ describe("CookieConsentBannerLoader", () => {
     });
   });
 });
+
+// ---------------------------------------------------------------------------
+// CookieConsentBanner — axe a11y (WCAG 2.2 AA)
+// ---------------------------------------------------------------------------
+describe("CookieConsentBanner — axe a11y", () => {
+  it("modal variant has no axe violations", async () => {
+    const { container } = renderWithProviders(
+      <CookieConsentBanner variant="modal" />,
+    );
+    const results = await axe(container);
+    expect(results).toHaveNoViolations();
+  });
+
+  it("banner variant has no axe violations", async () => {
+    const { container } = renderWithProviders(
+      <CookieConsentBanner variant="banner" />,
+    );
+    const results = await axe(container);
+    expect(results).toHaveNoViolations();
+  });
+});