Add Playwright test artifacts to .gitignore

Playwright generates test-results/ and playwright-report/ directories
when running e2e tests. These should not be committed to the repository.

Added to frontend/.gitignore:
- /test-results/
- /playwright-report/
- /playwright/.cache/

https://claude.ai/code/session_01T57NPQfoRb2fS7ihdWkTxq

frontend/.gitignore

@@ -12,6 +12,9 @@
 
 # testing
 /coverage
+/test-results/
+/playwright-report/
+/playwright/.cache/
 
 # next.js
 /.next/