IAV-1048 : Payment methods integration with security fixes
- Add payment methods list to subscription preview and set default functionality
- Create StripeSubscriptionHelper component to centralize utility methods
- Fix SQL injection in findCustomerByEmail() - escape special characters
- Prevent NPE in mapPaymentMethodToInfo() - add null safety checks
- Fix exception type consistency in setDefaultPaymentMethod()
- Add null check for price unit amount calculation
- Extract constants for API limits
- Remove emojis from production logs
Closes IAV-1048