chore: Remove .next from git tracking and add .prod.env to gitignore

- Remove .next folder from git tracking (build artifacts should not be versioned)
- Add .prod.env to gitignore for production environment configuration

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

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

.gitignore

@@ -28,6 +28,7 @@ yarn-error.log*
 .env
 .env*.local
 .env.test
+.prod.env
 
 # vercel
 .vercel