chore: ignore root-level vendor/ directory

Stray PHP vendor dir created by a composer require run outside erp/.
The Laravel app lives in erp/ — its own vendor/ is already gitignored.

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

Author: claude

.gitignore

@@ -15,3 +15,6 @@ yarn-error.log*
 .claude/
 .env.bak
 *.env.bak
+
+# Stray PHP vendor dir
+vendor/