refac: register only open while no verified acc exists, enforced by a use case rather than handler & sends verification email whose link uses the conf pub URL whose code expires after 2h

internal/domain/user/userDomain.go

@@ -7,6 +7,7 @@ import (
 
 var ErrUserNotFound = errors.New("user not found")
 var ErrInvalidCredentials = errors.New("invalid credentials")
+var ErrRegistrationClosed = errors.New("registration closed")
 
 type User struct {
 	ID                     uint32    `json:"id"`