fix(test): add missing stub methods for RedeemCodeRepository and AdminService

Add ListByUserPaginated and SumPositiveBalanceByUser to redeemRepoStub
Add GetUserBalanceHistory to stubAdminService

Fixes CI test compilation errors

backend/internal/service/admin_service_search_test.go

@@ -152,6 +152,14 @@ func (s *redeemRepoStubForAdminList) ListWithFilters(_ context.Context, params p
 	return s.listWithFiltersCodes, result, nil
 }
 
+func (s *redeemRepoStubForAdminList) ListByUserPaginated(_ context.Context, userID int64, params pagination.PaginationParams, codeType string) ([]RedeemCode, *pagination.PaginationResult, error) {
+	panic("unexpected ListByUserPaginated call")
+}
+
+func (s *redeemRepoStubForAdminList) SumPositiveBalanceByUser(_ context.Context, userID int64) (float64, error) {
+	panic("unexpected SumPositiveBalanceByUser call")
+}
+
 func TestAdminService_ListAccounts_WithSearch(t *testing.T) {
 	t.Run("search 参数正常传递到 repository 层", func(t *testing.T) {
 		repo := &accountRepoStubForAdminList{