feat: add Role (owner|admin) to the user domain, persistence model and mapper

test/user_response_field_hygiene_test.go

@@ -125,7 +125,7 @@ func TestUserResponseFieldHygiene(t *testing.T) {
 			t.Fatalf("failed to decode response: %v", err)
 		}
 
-		expectedKeys := []string{"id", "username", "email", "is_verified", "created_at", "updated_at", "display_name"}
+		expectedKeys := []string{"id", "username", "email", "is_verified", "created_at", "updated_at", "display_name", "role"}
 		if len(decoded) != len(expectedKeys) {
 			t.Errorf("expected exactly %d keys, got %d: %v", len(expectedKeys), len(decoded), decoded)
 		}