fix: add missing ERP_AUTO_CLOSE_BROWSER to .env.example

- Document ERP_AUTO_CLOSE_BROWSER environment variable
- This variable is used in test scripts to control browser auto-close behavior
- Ensures template is complete with all used variables

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -9,3 +9,4 @@ ERP_PASSWORD=your_password
 # Browser Behavior
 ERP_HEADLESS=false
 ERP_IGNORE_HTTPS_ERRORS=true
+ERP_AUTO_CLOSE_BROWSER=true