chore: ignore the .vitest artifact directory

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: kanadgupta

.gitignore

@@ -23,3 +23,6 @@ packages/cli-*/bin/
 
 # Turbo
 .turbo/
+
+# Vitest 5 artifact directory (blob reports, attachments, html/json output)
+.vitest/