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/.bin/playwright

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+../@playwright/test/cli.js

frontend/e2e/node_modules/.bin/playwright-core

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+../playwright-core/cli.js

frontend/e2e/node_modules/.bin/tsc

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+../typescript/bin/tsc

frontend/e2e/node_modules/.bin/tsserver

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+../typescript/bin/tsserver