chore: gitignore Playwright test screenshots

Add specific patterns for root-directory PNG files generated during
E2E testing (step*.png, dialog*.png, regression*.png, etc.) and
tests/test_peer_review.py. Uses path-prefixed patterns to avoid
ignoring tracked PNGs in subdirectories (favicons, logos).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: RyanKim17920

.gitignore

@@ -241,4 +241,18 @@ dist-ssr
 # Test output
 test-results/
 playwright-report/
-.playwright-mcp
+.playwright-mcp
+
+# Test artifacts
+# Playwright test screenshots (root directory only)
+/step*.png
+/dialog*.png
+/login*.png
+/paper*.png
+/final*.png
+/regression*.png
+/reviewers*.png
+/contributors*.png
+
+# Test files
+tests/test_peer_review.py