feat(支付): 添加Apple应用内支付支持

- 在CheckoutOrderResponse结构中添加product_ids字段用于存储Apple IAP产品ID
- 新增AppleIAP支付平台常量及映射
- 实现Apple IAP支付处理逻辑，生成对应的产品ID

pkg/payment/platform.go

@@ -10,6 +10,7 @@ const (
 	EPay
 	Balance
 	CryptoSaaS
+	AppleIAP
 	UNSUPPORTED Platform = -1
 )
 
@@ -19,6 +20,8 @@ var platformNames = map[string]Platform{
 	"AlipayF2F":   AlipayF2F,
 	"EPay":        EPay,
 	"balance":     Balance,
+	"AppleIAP":    AppleIAP,
+	"apple_iap":   AppleIAP,
 	"unsupported": UNSUPPORTED,
 }
 
@@ -80,5 +83,12 @@ func GetSupportedPlatforms() []types.PlatformInfo {
 				"secret_key": "Secret Key",
 			},
 		},
+		{
+			Platform:    AppleIAP.String(),
+			PlatformUrl: "https://developer.apple.com/in-app-purchase/",
+			PlatformFieldDescription: map[string]string{
+				"product_ids": "Apple In-App Purchase product ids (merchant.hifastvpn.day${quantity})",
+			},
+		},
 	}
 }