fix(poll): Series 删除前检查关联套餐 POLL-04

- package_store.go 新增 CountBySeriesID 方法，统计指定系列下的活跃套餐数量
- package_series/service.go Service 注入 packageStore 字段，Delete 前调用 CountBySeriesID 检查
- bootstrap/services.go 更新 PackageSeries 服务初始化，传入 PackageStore

internal/store/postgres/package_store.go

@@ -8,6 +8,7 @@ import (
 	"github.com/break/junhong_cmp_fiber/internal/model"
 	"github.com/break/junhong_cmp_fiber/internal/store"
 	"github.com/break/junhong_cmp_fiber/pkg/constants"
+	"github.com/break/junhong_cmp_fiber/pkg/errors"
 	"github.com/break/junhong_cmp_fiber/pkg/middleware"
 )
 
@@ -135,3 +136,15 @@ func (s *PackageStore) GetByIDsUnscoped(ctx context.Context, ids []uint) ([]*mod
 	}
 	return packages, nil
 }
+
+// CountBySeriesID 统计指定系列下的活跃套餐数量（未软删除）
+func (s *PackageStore) CountBySeriesID(ctx context.Context, seriesID uint) (int64, error) {
+	var count int64
+	err := s.db.WithContext(ctx).Model(&model.Package{}).
+		Where("series_id = ? AND deleted_at IS NULL", seriesID).
+		Count(&count).Error
+	if err != nil {
+		return 0, errors.Wrap(errors.CodeDatabaseError, err, "统计关联套餐失败")
+	}
+	return count, nil
+}