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/admin-dashboard.spec.ts

@@ -9,7 +9,7 @@ import { setupSuperuserMocks, loginViaUI } from './helpers/auth';
 test.describe('Admin Dashboard - Page Load', () => {
   test.beforeEach(async ({ page }) => {
     await setupSuperuserMocks(page);
-    await loginViaUI(page);
+    // Auth already cached in storage state (loginViaUI removed for performance)
     await page.goto('/admin');
   });
 
@@ -28,7 +28,7 @@ test.describe('Admin Dashboard - Page Load', () => {
 test.describe('Admin Dashboard - Statistics Cards', () => {
   test.beforeEach(async ({ page }) => {
     await setupSuperuserMocks(page);
-    await loginViaUI(page);
+    // Auth already cached in storage state (loginViaUI removed for performance)
     await page.goto('/admin');
   });
 
@@ -61,7 +61,7 @@ test.describe('Admin Dashboard - Statistics Cards', () => {
 test.describe('Admin Dashboard - Quick Actions', () => {
   test.beforeEach(async ({ page }) => {
     await setupSuperuserMocks(page);
-    await loginViaUI(page);
+    // Auth already cached in storage state (loginViaUI removed for performance)
     await page.goto('/admin');
   });
 
@@ -107,7 +107,7 @@ test.describe('Admin Dashboard - Quick Actions', () => {
 test.describe('Admin Dashboard - Analytics Charts', () => {
   test.beforeEach(async ({ page }) => {
     await setupSuperuserMocks(page);
-    await loginViaUI(page);
+    // Auth already cached in storage state (loginViaUI removed for performance)
     await page.goto('/admin');
   });
 
@@ -152,7 +152,7 @@ test.describe('Admin Dashboard - Analytics Charts', () => {
 test.describe('Admin Dashboard - Accessibility', () => {
   test.beforeEach(async ({ page }) => {
     await setupSuperuserMocks(page);
-    await loginViaUI(page);
+    // Auth already cached in storage state (loginViaUI removed for performance)
     await page.goto('/admin');
   });