Refactor Playwright tests to use cached authentication state for improved performance

- Removed redundant `loginViaUI` calls across E2E tests, leveraging cached storage state for faster test execution.
- Enhanced Playwright configuration to include a `setup` project for pre-caching admin and regular user authentication states.
- Added new `auth.setup.ts` to handle initial authentication and save storage states to `.auth` directory.
- Increased local worker count to 16 (CI unchanged) to optimize parallel execution.
- Updated `.gitignore` to exclude authentication state files.

frontend/e2e/auth.setup.ts

@@ -0,0 +1,70 @@
+/**
+ * Authentication Setup for Playwright Tests
+ *
+ * This file sets up authenticated browser states that can be reused across tests.
+ * Instead of logging in via UI for every test (5-7s overhead), we login once per
+ * worker and save the storage state (cookies, localStorage) to disk.
+ *
+ * Performance Impact:
+ * - Before: 133 tests × 5-7s login = ~700s overhead
+ * - After: 2 logins (once per role) × 5s = ~10s overhead
+ * - Savings: ~690s (~11 minutes) per test run
+ */
+
+import { test as setup, expect } from '@playwright/test';
+import path from 'path';
+import { setupAuthenticatedMocks, setupSuperuserMocks, loginViaUI } from './helpers/auth';
+
+// Use absolute paths to ensure correct file location
+const ADMIN_STORAGE_STATE = path.join(__dirname, '.auth', 'admin.json');
+const USER_STORAGE_STATE = path.join(__dirname, '.auth', 'user.json');
+
+/**
+ * Setup: Authenticate as admin/superuser
+ * This runs ONCE before all admin tests
+ */
+setup('authenticate as admin', async ({ page }) => {
+  // Set up API mocks for superuser
+  await setupSuperuserMocks(page);
+
+  // Login via UI (one time only)
+  await loginViaUI(page);
+
+  // Verify we're actually logged in
+  await page.goto('/settings');
+  await page.waitForSelector('h1:has-text("Settings")', { timeout: 10000 });
+
+  // Verify admin access
+  const adminLink = page.locator('header nav').getByRole('link', { name: 'Admin', exact: true });
+  await expect(adminLink).toBeVisible();
+
+  // Save authenticated state to file
+  await page.context().storageState({ path: ADMIN_STORAGE_STATE });
+
+  console.log('✅ Admin authentication state saved to:', ADMIN_STORAGE_STATE);
+});
+
+/**
+ * Setup: Authenticate as regular user
+ * This runs ONCE before all user tests
+ */
+setup('authenticate as regular user', async ({ page }) => {
+  // Set up API mocks for regular user
+  await setupAuthenticatedMocks(page);
+
+  // Login via UI (one time only)
+  await loginViaUI(page);
+
+  // Verify we're actually logged in
+  await page.goto('/settings');
+  await page.waitForSelector('h1:has-text("Settings")', { timeout: 10000 });
+
+  // Verify NOT admin (regular user)
+  const adminLink = page.locator('header nav').getByRole('link', { name: 'Admin', exact: true });
+  await expect(adminLink).not.toBeVisible();
+
+  // Save authenticated state to file
+  await page.context().storageState({ path: USER_STORAGE_STATE });
+
+  console.log('✅ Regular user authentication state saved to:', USER_STORAGE_STATE);
+});