- Add bluemonday import to auth.go and subscriber.go
- Add UGCPolicy sanitization for username, email, firstName, lastName, and role in Register
- Add conditional XSS sanitization for firstName, lastName, email, and MSISDN in CreateSubscriber and UpdateSubscriber
- Replace Page and PageSize with Cursor and Limit in ListSubscribers query parameters
- Add HATEOAS links to CreateSubscriber, GetSubscriber
- Add AuthHandler struct with authService dependency and NewAuthHandler constructor
- Add LoginRequest/LoginResponse/RegisterRequest/ChangePasswordRequest structs with validation tags
- Add Login method with username/password validation, token generation, and user response
- Add Register method with email/password/role validation and user creation
- Add RefreshToken method with JWT refresh token validation