Add Jest setup file with proper mocks

jest.setup.ts

@@ -0,0 +1,26 @@
+import '@testing-library/jest-dom';
+import {jest} from '@jest/globals';
+
+// Mock window.matchMedia
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: jest.fn().mockImplementation(query => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: jest.fn(),
+    removeListener: jest.fn(),
+    addEventListener: jest.fn(),
+    removeEventListener: jest.fn(),
+    dispatchEvent: jest.fn(),
+  })),
+});
+
+// Mock Docusaurus context
+Object.defineProperty(window, 'docusaurus', {
+  value: {
+    prefetch: jest.fn(),
+    preload: jest.fn(),
+  },
+  configurable: true,
+});