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/node_modules/playwright/NOTICE

@@ -0,0 +1,5 @@
+Playwright
+Copyright (c) Microsoft Corporation
+
+This software contains code derived from the Puppeteer project (https://github.com/puppeteer/puppeteer),
+available under the Apache 2.0 license (https://github.com/puppeteer/puppeteer/blob/master/LICENSE).