Connect sign-up to Sendico Facts intake (#46)

frontend/packages/sxchnge_auth/lib/src/mappers/backend.dart

@@ -2,6 +2,7 @@ import '../dto/backend.dart';
 import '../models/auth.dart';
 import '../models/session.dart';
 import '../models/two_factor.dart';
+import '../models/verification.dart';
 
 abstract final class BackendMapper {
   static AuthResult signup(BackendDTO dto) {
@@ -33,11 +34,19 @@ abstract final class BackendMapper {
   static AuthException authFailure(int status, BackendDTO dto) =>
       AuthException(switch (dto.error) {
         'email_in_use' => AuthError.emailInUse,
+        'signup_attention_required' => AuthError.signupNeedsAssistance,
         'account_not_verified' => AuthError.accountNotVerified,
         _ when status == 401 => AuthError.invalidCredentials,
         _ when status == 429 => AuthError.factorCooldown,
         _ => AuthError.unavailable,
       });
+  static VerificationException verificationFailure(BackendDTO dto) =>
+      VerificationException(switch (dto.error) {
+        'expired' => VerificationError.expired,
+        'invalid' => VerificationError.invalid,
+        'signup_attention_required' => VerificationError.needsAssistance,
+        _ => VerificationError.internal,
+      });
   static FactorException factorFailure(int status, BackendDTO dto) =>
       FactorException(switch (dto.error) {
         'expired' => FactorError.expired,