fix: EmailManager route calls get_email_users not get_users

The method is named get_email_users in EmailManager; the route was
calling the non-existent get_users, causing an AttributeError on every
GET /api/email/users request.

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

api/routes/email.py

@@ -11,7 +11,7 @@ def get_email_users():
     """Get email users."""
     try:
         from app import email_manager
-        users = email_manager.get_users()
+        users = email_manager.get_email_users()
         return jsonify(users)
     except Exception as e:
         logger.error(f"Error getting email users: {e}")