修复(#128): 按规则类型决定促销资格，让 InactiveUser/Campaign 对老用户生效

此前 calculatePurchasePrice 把 allowPromo 绑死在 orderType == 1，导致只要用户
有任何过往付费订阅（含已过期），就会被 paidSubscriptionQuery 路由为续费
（orderType=2），跳过所有促销评估。后果：

  - InactiveUser 召回促销永远无法触发（其目标人群恰好就是有过期订阅的用户）
  - Campaign 全员活动对老用户 / 升级加购场景完全失效
  - 套餐列表（loadSubscribePromoMap）直接调 EvaluatePromo 不感知 orderType，
    可能显示促销价但下单时却拿到原价

修复方式：把 isFirstPurchase 下放给 EvaluatePromo，由规则类型决定 gating：

  - NewUser    要求 isFirstPurchase=true（保留首购语义）
  - InactiveUser 由规则自身的"上次订阅过期 N 月以上"条件判定
  - Campaign   时间窗内对任意用户生效

新增 common.HasPaidSubscription 助手，套餐列表与下单走同一份 isFirstPurchase
判定，确保展示价与实际下单价口径一致。

测试：补充 EvaluatePromo / calculatePurchasePrice 的 NewUser 屏蔽 + Campaign
放开用例；更新 loadSubscribePromoMap 测试覆盖新增 HasPaidSubscription 查询。

注：renewalLogic.go 仍未接入促销（属于方向 B 的彻底统一，本次未涵盖）。

internal/logic/common/promoEligibility.go

@@ -28,7 +28,16 @@ type promoRuleParams struct {
 	InactiveMonths int `json:"inactive_months"`
 }
 
-func EvaluatePromo(ctx context.Context, svcCtx *svc.ServiceContext, userID int64, subscribeID int64, quantity int64) (*PromoResult, error) {
+// EvaluatePromo decides whether the given (user, subscribe, quantity) tuple
+// qualifies for any active promo rule. Each rule type has its own gating:
+//   - new_user: requires isFirstPurchase=true (no prior paid subscription)
+//   - inactive_user: requires a previously expired subscription (rule self-check)
+//   - campaign: applies unconditionally within the configured time window
+//
+// Pass isFirstPurchase=true on order paths where the request is being routed
+// as a brand-new purchase; pass false when the user already has a paid
+// subscription (including expired ones) so NewUser cannot be reused.
+func EvaluatePromo(ctx context.Context, svcCtx *svc.ServiceContext, userID int64, subscribeID int64, quantity int64, isFirstPurchase bool) (*PromoResult, error) {
 	result := &PromoResult{}
 	if svcCtx == nil || svcCtx.PromoModel == nil || svcCtx.DB == nil || subscribeID <= 0 || quantity <= 0 {
 		return result, nil
@@ -59,7 +68,7 @@ func EvaluatePromo(ctx context.Context, svcCtx *svc.ServiceContext, userID int64
 			}
 		}
 
-		eligible, expiresAt, err := evaluatePromoRule(ctx, svcCtx.DB, rule, params, userID, &currentUser, now)
+		eligible, expiresAt, err := evaluatePromoRule(ctx, svcCtx.DB, rule, params, userID, isFirstPurchase, &currentUser, now)
 		if err != nil {
 			return nil, err
 		}
@@ -96,12 +105,13 @@ func evaluatePromoRule(
 	rule *promo.RuleWithPrice,
 	params promoRuleParams,
 	userID int64,
+	isFirstPurchase bool,
 	currentUser *user.User,
 	now time.Time,
 ) (bool, time.Time, error) {
 	switch rule.Type {
 	case promo.RuleTypeNewUser:
-		if userID <= 0 {
+		if userID <= 0 || !isFirstPurchase {
 			return false, time.Time{}, nil
 		}
 		return evaluateNewUserPromo(ctx, db, params, userID, currentUser, now)