Add E2E tests for internationalization across multiple pages

- Implemented navigation.spec.ts to test language switching and translation of navigation elements.
- Created sessions-page.spec.ts to verify translations on the sessions page, including headers, status badges, and date formatting.
- Developed settings-page.spec.ts to ensure settings page content is translated and persists across sessions.
- Added skills-page.spec.ts to validate translations for skill categories, action buttons, and empty states.

ccw/frontend/src/test/setup.ts

@@ -0,0 +1,62 @@
+// ========================================
+// Test Setup
+// ========================================
+// Global test configuration for Vitest
+
+import { afterEach, beforeEach, vi } from 'vitest';
+import { cleanup } from '@testing-library/react';
+import '@testing-library/jest-dom/vitest';
+
+// Cleanup after each test
+afterEach(() => {
+  cleanup();
+});
+
+// Mock window.matchMedia for theme detection
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation((query: string) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});
+
+// Mock localStorage
+const localStorageMock = (() => {
+  let store: Record<string, string> = {};
+
+  return {
+    getItem: (key: string) => store[key] ?? null,
+    setItem: (key: string, value: string) => {
+      store[key] = value.toString();
+    },
+    removeItem: (key: string) => {
+      delete store[key];
+    },
+    clear: () => {
+      store = {};
+    },
+  };
+})();
+
+Object.defineProperty(global, 'localStorage', {
+  value: localStorageMock,
+});
+
+// Reset all mocks before each test
+beforeEach(() => {
+  vi.clearAllMocks();
+  localStorageMock.clear();
+});
+
+// Mock browser APIs not available in jsdom (for Radix UI components)
+Element.prototype.scrollIntoView = vi.fn();
+Element.prototype.hasPointerCapture = vi.fn(() => false);
+Element.prototype.setPointerCapture = vi.fn();
+Element.prototype.releasePointerCapture = vi.fn();