fix(tests): resolve failing go tests and segfaults due to missing mock interface implementations

- MockKratosAdminService 및 MockTenantService에 새로 추가된 인터페이스 메소드(CreateUser, ListIdentitySessions 등) 구현 추가
- 회원가입 테스트(auth_handler_signup_test.go) 시, isAffiliateTenant 검증 과정에서 TenantService가 nil일 때 발생하는 segfault 방지 로직 보강
- Mock 객체 반환값 타입 불일치 및 testify/mock 매개변수 에러 등 테스트 의존성 전반 수정

backend/internal/service/kratos_admin_service.go

@@ -51,6 +51,9 @@ type KratosAdminService interface {
 	UpdateIdentityPassword(ctx context.Context, identityID, newPassword string) error
 	DeleteIdentity(ctx context.Context, identityID string) error
 	CreateUser(ctx context.Context, user *domain.BrokerUser, password string) (string, error)
+	ListIdentitySessions(ctx context.Context, identityID string) ([]KratosSession, error)
+	GetSession(ctx context.Context, sessionID string) (*KratosSession, error)
+	DeleteSession(ctx context.Context, sessionID string) error
 }
 
 type kratosAdminService struct {
@@ -367,3 +370,88 @@ func getenvKratos(key, fallback string) string {
 	}
 	return fallback
 }
+
+func (s *kratosAdminService) ListIdentitySessions(ctx context.Context, identityID string) ([]KratosSession, error) {
+	url := fmt.Sprintf("%s/admin/identities/%s/sessions", s.AdminURL, identityID)
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	client := s.HTTPClient
+	if client == nil {
+		client = http.DefaultClient
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == http.StatusNotFound {
+		return []KratosSession{}, nil
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status: %d", resp.StatusCode)
+	}
+
+	var sessions []KratosSession
+	if err := json.NewDecoder(resp.Body).Decode(&sessions); err != nil {
+		return nil, err
+	}
+	return sessions, nil
+}
+
+func (s *kratosAdminService) GetSession(ctx context.Context, sessionID string) (*KratosSession, error) {
+	url := fmt.Sprintf("%s/admin/sessions/%s", s.AdminURL, sessionID)
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	client := s.HTTPClient
+	if client == nil {
+		client = http.DefaultClient
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == http.StatusNotFound {
+		return nil, nil
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status: %d", resp.StatusCode)
+	}
+
+	var session KratosSession
+	if err := json.NewDecoder(resp.Body).Decode(&session); err != nil {
+		return nil, err
+	}
+	return &session, nil
+}
+
+func (s *kratosAdminService) DeleteSession(ctx context.Context, sessionID string) error {
+	url := fmt.Sprintf("%s/admin/sessions/%s", s.AdminURL, sessionID)
+	req, err := http.NewRequestWithContext(ctx, "DELETE", url, nil)
+	if err != nil {
+		return err
+	}
+
+	client := s.HTTPClient
+	if client == nil {
+		client = http.DefaultClient
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusNoContent && resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unexpected status: %d", resp.StatusCode)
+	}
+	return nil
+}

backend/internal/service/mock_common_test.go

@@ -116,3 +116,13 @@ func (m *MockKratosAdminServiceShared) CreateUser(ctx context.Context, user *dom
 	args := m.Called(ctx, user, password)
 	return args.String(0), args.Error(1)
 }
+
+func (m *MockKratosAdminServiceShared) ListIdentitySessions(ctx context.Context, identityID string) ([]KratosSession, error) {
+	return nil, nil
+}
+func (m *MockKratosAdminServiceShared) GetSession(ctx context.Context, sessionID string) (*KratosSession, error) {
+	return nil, nil
+}
+func (m *MockKratosAdminServiceShared) DeleteSession(ctx context.Context, sessionID string) error {
+	return nil
+}

backend/internal/service/org_chart_service_test.go

@@ -237,3 +237,13 @@ func TestImportOrgChart_MessyHeader(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotNil(t, res)
 }
+
+func (m *mockKratosService) ListIdentitySessions(ctx context.Context, identityID string) ([]KratosSession, error) {
+	return nil, nil
+}
+func (m *mockKratosService) GetSession(ctx context.Context, sessionID string) (*KratosSession, error) {
+	return nil, nil
+}
+func (m *mockKratosService) DeleteSession(ctx context.Context, sessionID string) error {
+	return nil
+}