💸 chore: Align subscription pricing display with global currency settings

Unify subscription price rendering to use the site-wide currency symbol/rate on the wallet and admin views.
Make subscription plan currency read-only in the editor and force USD on create/update to avoid drift.
Use global currency display type when creating Creem checkout payloads.

controller/subscription.go

@@ -149,6 +149,7 @@ func AdminCreateSubscriptionPlan(c *gin.Context) {
 	if req.Plan.Currency == "" {
 		req.Plan.Currency = "USD"
 	}
+	req.Plan.Currency = "USD"
 	if req.Plan.DurationUnit == "" {
 		req.Plan.DurationUnit = model.SubscriptionDurationMonth
 	}
@@ -215,6 +216,7 @@ func AdminUpdateSubscriptionPlan(c *gin.Context) {
 	if req.Plan.Currency == "" {
 		req.Plan.Currency = "USD"
 	}
+	req.Plan.Currency = "USD"
 	if req.Plan.DurationUnit == "" {
 		req.Plan.DurationUnit = model.SubscriptionDurationMonth
 	}

controller/subscription_payment_creem.go

@@ -9,6 +9,7 @@ import (
 	"github.com/QuantumNous/new-api/common"
 	"github.com/QuantumNous/new-api/model"
 	"github.com/QuantumNous/new-api/setting"
+	"github.com/QuantumNous/new-api/setting/operation_setting"
 	"github.com/gin-gonic/gin"
 	"github.com/thanhpk/randstr"
 )
@@ -74,11 +75,20 @@ func SubscriptionRequestCreemPay(c *gin.Context) {
 	}
 
 	// Reuse Creem checkout generator by building a lightweight product reference.
+	currency := "USD"
+	switch operation_setting.GetGeneralSetting().QuotaDisplayType {
+	case operation_setting.QuotaDisplayTypeCNY:
+		currency = "CNY"
+	case operation_setting.QuotaDisplayTypeUSD:
+		currency = "USD"
+	default:
+		currency = "USD"
+	}
 	product := &CreemProduct{
 		ProductId: plan.CreemProductId,
 		Name:      plan.Title,
 		Price:     plan.PriceAmount,
-		Currency:  plan.Currency,
+		Currency:  currency,
 		Quota:     0,
 	}