Implement comprehensive frontend integration testing with Playwright

- Add Playwright E2E testing framework with cross-browser support (Chrome, Firefox)
- Create authentication helpers for CalDAV server integration
- Implement calendar interaction helpers with event creation, drag-and-drop, and view switching
- Add comprehensive drag-and-drop test suite with event cleanup
- Configure CI/CD integration with Gitea Actions for headless testing
- Support both local development and CI environments with proper dependency management
- Include video recording, screenshots, and HTML reporting for test debugging
- Handle Firefox-specific timing and interaction challenges with force clicks and timeouts

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/e2e/tests/auth.spec.ts

@@ -0,0 +1,44 @@
+import { test, expect } from '@playwright/test';
+
+test.describe('Authentication', () => {
+  test('should show login form initially', async ({ page }) => {
+    await page.goto('/');
+    
+    // Should redirect to login page
+    await expect(page).toHaveURL(/.*\/login/);
+    
+    // Check for login form elements
+    await expect(page.getByLabel('CalDAV Server URL')).toBeVisible();
+    await expect(page.getByRole('textbox', { name: 'Username' })).toBeVisible();
+    await expect(page.getByLabel('Password')).toBeVisible();
+    await expect(page.getByRole('button', { name: 'Sign In' })).toBeVisible();
+  });
+
+  test('should show validation errors for empty form', async ({ page }) => {
+    await page.goto('/login');
+    
+    // Try to submit empty form
+    await page.getByRole('button', { name: 'Sign In' }).click();
+    
+    // Should show validation errors
+    await expect(page.getByText('Please fill in all fields')).toBeVisible();
+  });
+
+  test('should handle invalid credentials', async ({ page }) => {
+    await page.goto('/login');
+    
+    // Fill in invalid credentials
+    await page.getByLabel('CalDAV Server URL').fill('https://invalid-server.com');
+    await page.getByRole('textbox', { name: 'Username' }).fill('invalid-user');
+    await page.getByLabel('Password').fill('invalid-password');
+    
+    // Submit form
+    await page.getByRole('button', { name: 'Sign In' }).click();
+    
+    // Should show error message (wait for loading to finish first)
+    await expect(page.getByRole('button', { name: 'Sign In' })).toBeVisible(); // Wait for loading to finish
+    
+    // Check for any error message in the error-message div
+    await expect(page.locator('.error-message')).toBeVisible();
+  });
+});