Add comprehensive test suite infrastructure

- Create backend xUnit test project with Moq and FluentAssertions
- Add test utilities: TestDataFactory, MockHttpContext, TestUserClaims
- Create AuthControllerTests with comprehensive auth scenarios
- Install Jest and React Testing Library for frontend
- Configure jest.config.ts and jest.setup.ts with Next.js support
- Add test scripts to package.json

frontend/jest.setup.ts

@@ -0,0 +1,62 @@
+import '@testing-library/jest-dom';
+
+// Mock Next.js router
+jest.mock('next/navigation', () => ({
+  useRouter() {
+    return {
+      route: '/',
+      pathname: '/',
+      query: {},
+      asPath: '/',
+      push: jest.fn(),
+      replace: jest.fn(),
+      reload: jest.fn(),
+      back: jest.fn(),
+      prefetch: jest.fn(),
+      beforePopState: jest.fn(),
+      events: {
+        on: jest.fn(),
+        off: jest.fn(),
+        emit: jest.fn(),
+      },
+      isFallback: false,
+      isLocaleDomain: false,
+      isReady: true,
+      isPreview: false,
+    };
+  },
+  useSearchParams() {
+    return {
+      get: jest.fn(),
+      getAll: jest.fn(),
+      has: jest.fn(),
+      entries: jest.fn(),
+      keys: jest.fn(),
+      values: jest.fn(),
+      forEach: jest.fn(),
+    };
+  },
+  usePathname() {
+    return '/';
+  },
+}));
+
+// 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(),
+  })),
+});
+
+// Clean up after each test
+afterEach(() => {
+  jest.clearAllMocks();
+});