feat(payment): add complete payment system with multi-provider support

Add a full payment and subscription system supporting EasyPay (Alipay/WeChat),
Stripe, and direct Alipay/WeChat Pay providers with multi-instance load balancing.

backend/ent/user/where.go

@@ -1067,6 +1067,29 @@ func HasPromoCodeUsagesWith(preds ...predicate.PromoCodeUsage) predicate.User {
 	})
 }
 
+// HasPaymentOrders applies the HasEdge predicate on the "payment_orders" edge.
+func HasPaymentOrders() predicate.User {
+	return predicate.User(func(s *sql.Selector) {
+		step := sqlgraph.NewStep(
+			sqlgraph.From(Table, FieldID),
+			sqlgraph.Edge(sqlgraph.O2M, false, PaymentOrdersTable, PaymentOrdersColumn),
+		)
+		sqlgraph.HasNeighbors(s, step)
+	})
+}
+
+// HasPaymentOrdersWith applies the HasEdge predicate on the "payment_orders" edge with a given conditions (other predicates).
+func HasPaymentOrdersWith(preds ...predicate.PaymentOrder) predicate.User {
+	return predicate.User(func(s *sql.Selector) {
+		step := newPaymentOrdersStep()
+		sqlgraph.HasNeighborsWith(s, step, func(s *sql.Selector) {
+			for _, p := range preds {
+				p(s)
+			}
+		})
+	})
+}
+
 // HasUserAllowedGroups applies the HasEdge predicate on the "user_allowed_groups" edge.
 func HasUserAllowedGroups() predicate.User {
 	return predicate.User(func(s *sql.Selector) {