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/test-results/.last-run.json

@@ -0,0 +1,13 @@
+{
+  "status": "failed",
+  "failedTests": [
+    "24855026d04571c6a5d5-9bacc499103cd0a345ec",
+    "24855026d04571c6a5d5-24030ee34fc1fbef7226",
+    "24855026d04571c6a5d5-064a99c6585d1deec16d",
+    "24855026d04571c6a5d5-12309e761c90483f2f3c",
+    "1cb75a6647e074915eb0-f001aeb5f3bfa881a3c6",
+    "1cb75a6647e074915eb0-b8371670584fb07223ae",
+    "24855026d04571c6a5d5-6bda6cc88e326d44736a",
+    "24855026d04571c6a5d5-c10ea9f39dfab5618a29"
+  ]
+}