chore: add .env.vercel.* to gitignore

Prevent accidental commits of Vercel environment files.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: iamjr15

.gitignore

@@ -271,3 +271,4 @@ another app - backend/
 another app - frontend/
 .vercel
 .env*.local
+.env.vercel.*