fix: add root test-results/ to gitignore

Playwright outputs test-results/ at the repo root when run from
there. frontend/test-results/ was already ignored but the root
directory was not.

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

Author: wesm

.gitignore

@@ -8,6 +8,7 @@
 node_modules/
 frontend/dist/
 frontend/test-results/
+test-results/
 frontend/playwright-report/
 
 # Embedded frontend build output