chore(01-01): ignore frontend test artifacts

- Add frontend/coverage/ for Vitest coverage reports
- Add frontend/playwright-report/ for Playwright HTML reports
- Add frontend/test-results/ for Playwright test results

.gitignore

@@ -32,3 +32,7 @@ static/custom/*
 static/dist/
 .planning
 .coverage
+# Frontend test artifacts
+frontend/coverage/
+frontend/playwright-report/
+frontend/test-results/