- Add OnboardingValidator struct with ValidateRequest and ValidateMVNO methods in validator.go
- Add business info validation with name length, ID format, email regex, and phone length checks
- Add plan validation with subscriber limits for Starter (1000) and Growth (10000) plans
- Add technical requirements validation with country code format and use case length checks
- Add compliance validation with country-specific regulatory checks and restricted country filtering
- Add technical feasibility validation
