查询绑定结果增加预期账号比对：mismatch 提前拦截

- 下单 data 传了 game_account 时，bind-result 返回 expected_game_account 与 mismatch
- 绑定账号与预期不一致时 message 提示，配合 submit 已有的一致性校验提前发现
- 对接文档补充 mismatch 字段与说明

backend/internal/service/delivery.go

@@ -128,14 +128,16 @@ type DeliveryProduct struct {
 }
 
 type DeliveryBindResult struct {
-	BindUUID    string `json:"bind_uuid"`
-	BindURL     string `json:"bind_url"`
-	QRURL       string `json:"qr_url"`
-	Bound       bool   `json:"bound"`
-	GameAccount string `json:"game_account,omitempty"`
-	RoleName    string `json:"role_name,omitempty"`
-	GameChannel string `json:"game_channel,omitempty"`
-	Message     string `json:"message,omitempty"`
+	BindUUID            string `json:"bind_uuid"`
+	BindURL             string `json:"bind_url"`
+	QRURL               string `json:"qr_url"`
+	Bound               bool   `json:"bound"`
+	GameAccount         string `json:"game_account,omitempty"`
+	RoleName            string `json:"role_name,omitempty"`
+	GameChannel         string `json:"game_channel,omitempty"`
+	ExpectedGameAccount string `json:"expected_game_account,omitempty"`
+	Mismatch            bool   `json:"mismatch,omitempty"`
+	Message             string `json:"message,omitempty"`
 }
 
 type DeliveryLinkResult struct {
@@ -220,14 +222,24 @@ func (s *DeliveryService) GetBindResult(merchantID uint, orderNo, bindUUID strin
 		}
 		return nil, err
 	}
-	return &DeliveryBindResult{
+	boundAccount := stringFromMap(account, "game_account")
+	result := &DeliveryBindResult{
 		BindUUID:    bindUUID,
 		Bound:       true,
-		GameAccount: stringFromMap(account, "game_account"),
+		GameAccount: boundAccount,
 		RoleName:    stringFromMap(account, "game_account_role_name"),
 		GameChannel: gameChannelText(account),
 		Message:     "绑定成功",
-	}, nil
+	}
+	// 下单时 data 透传的预期账号：绑定账号与预期不一致时提示，供自建页提前拦截。
+	if expected := requestDataString(order.RequestData, "game_account"); expected != "" {
+		result.ExpectedGameAccount = expected
+		if boundAccount != expected {
+			result.Mismatch = true
+			result.Message = "绑定成功，但绑定账号与下单预期账号不一致，请确认"
+		}
+	}
+	return result, nil
 }
 
 func (s *DeliveryService) bindWithOrder(orderNo, gameAccount string, auth *DeliveryLinkAuth, merchantID uint) (*DeliveryBindResult, error) {