feat: registrationBegin method without email;

fix: missing sqlc query parameter name;
feat: util for generating security codes;
feat: enums package

backend/internal/utils/enums/enums.go

@@ -0,0 +1,8 @@
+package enums
+
+type ConfirmationCodeType int32
+
+const (
+	RegistrationCodeType ConfirmationCodeType = iota
+	PasswordResetCodeType
+)