Implement verified public registration flow

src/user_engine/service.py

@@ -384,6 +384,8 @@ class UserEngineService:
             IdentityFactorType.EMAIL,
         ),
         correlation_id: str | None = None,
+        applicant_username: str | None = None,
+        client_id: str | None = None,
     ) -> RegistrationSession:
         tenant_context = self.resolve_tenant_context(actor, tenant)
         correlation_id = correlation_id or new_id("corr")
@@ -406,6 +408,8 @@ class UserEngineService:
             ),
             required_factor_types=required,
             started_by_subject=actor.subject,
+            applicant_username=applicant_username,
+            client_id=client_id,
             correlation_id=correlation_id,
         )
         with self.store.transaction():