fix(realname): ActivateByRealname 按 ExpiryBase 选择计时基准 REALNAME-04

- from_purchase：用 PackageUsage.CreatedAt（购买时刻）作为激活时间起点
- from_activation（默认）：用实名被触发的当前时刻作为激活时间起点

internal/service/package/activation_service.go

@@ -113,8 +113,14 @@ func (s *ActivationService) ActivateByRealname(ctx context.Context, carrierType
 				}
 			}
 
-			// 激活套餐
-			activatedAt := now
+			// REALNAME-04: 按 ExpiryBase 选择激活计时基准
+			// from_purchase：购买时起算，用 PackageUsage 创建时间；否则用实名触发当前时刻
+			var activatedAt time.Time
+			if pkg.ExpiryBase == "from_purchase" {
+				activatedAt = usage.CreatedAt
+			} else {
+				activatedAt = now
+			}
 			expiresAt := CalculateExpiryTime(pkg.CalendarType, activatedAt, pkg.DurationMonths, pkg.DurationDays)
 
 			// 计算下次重置时间