chore: add root test-results/ to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: etoyama

.gitignore

@@ -69,6 +69,7 @@ src/insight_blueprint/static/
 frontend/node_modules/
 
 # Playwright test artifacts
+test-results/
 frontend/test-results/
 frontend/playwright-report/