✨ chore: Improve subscription billing fallback and UI states

Add a lightweight active-subscription check to skip subscription pre-consume when none exist, reducing unnecessary transactions and locks. In the subscription UI, disable subscription-first options when no active plan is available, show the effective fallback to wallet with a clear notice, and distinguish “invalidated” from “expired” states. Update i18n strings across supported locales to reflect the new messages and status labels.

model/subscription.go

@@ -666,6 +666,22 @@ func GetAllActiveUserSubscriptions(userId int) ([]SubscriptionSummary, error) {
 	return buildSubscriptionSummaries(subs), nil
 }
 
+// HasActiveUserSubscription returns whether the user has any active subscription.
+// This is a lightweight existence check to avoid heavy pre-consume transactions.
+func HasActiveUserSubscription(userId int) (bool, error) {
+	if userId <= 0 {
+		return false, errors.New("invalid userId")
+	}
+	now := common.GetTimestamp()
+	var count int64
+	if err := DB.Model(&UserSubscription{}).
+		Where("user_id = ? AND status = ? AND end_time > ?", userId, "active", now).
+		Count(&count).Error; err != nil {
+		return false, err
+	}
+	return count > 0, nil
+}
+
 // GetAllUserSubscriptions returns all subscriptions (active and expired) for a user.
 func GetAllUserSubscriptions(userId int) ([]SubscriptionSummary, error) {
 	if userId <= 0 {