refactor: 删除 ports 目录

backend/internal/service/billing_cache_port.go

@@ -0,0 +1,15 @@
+package service
+
+import (
+	"time"
+)
+
+// SubscriptionCacheData represents cached subscription data
+type SubscriptionCacheData struct {
+	Status       string
+	ExpiresAt    time.Time
+	DailyUsage   float64
+	WeeklyUsage  float64
+	MonthlyUsage float64
+	Version      int64
+}