feat(api): 增强字段去重逻辑以支持易码通客户名称处理

在exports.go和templates.go中新增逻辑，确保在处理易码通数据时，若同时选择order.merchant_name与merchant.name，仅保留merchant.name。此改动提升了字段去重的准确性，确保返回的数据符合预期。

server/internal/api/exports.go

@@ -300,6 +300,34 @@ func (a *ExportsAPI) create(w http.ResponseWriter, r *http.Request) {
 			filtered = deduped
 		}
 	}
+	// 易码通客户名称字段去重：若同时选择 order.merchant_name 与 merchant.name，仅保留 merchant.name
+	if ds == "ymt" {
+		hasOrderMerchant := false
+		hasMerchantName := false
+		for _, tf := range filtered {
+			if tf == "order.merchant_name" {
+				hasOrderMerchant = true
+			}
+			if tf == "merchant.name" {
+				hasMerchantName = true
+			}
+		}
+		if hasOrderMerchant && hasMerchantName {
+			deduped := make([]string, 0, len(filtered))
+			removed := []string{}
+			for _, tf := range filtered {
+				if tf == "order.merchant_name" {
+					removed = append(removed, tf)
+					continue
+				}
+				deduped = append(deduped, tf)
+			}
+			if len(removed) > 0 {
+				logging.JSON("INFO", map[string]interface{}{"event": "fields_deduplicated_customer_name", "removed": removed, "reason": "易码通客户名称仅保留 merchant.name"})
+			}
+			filtered = deduped
+		}
+	}
 	labels := FieldLabels()
 	// 相同列名（中文标签）去重：如果多个表的字段共享同一列名，优先保留主表字段
 	{

server/internal/api/templates.go

@@ -120,6 +120,12 @@ func (a *TemplatesAPI) listTemplates(w http.ResponseWriter, r *http.Request) {
 			if !wl[tf] {
 				continue
 			}
+			// special dedupe: when both order.merchant_name and merchant.name exist, only count merchant.name
+			if ds == "ymt" && tf == "order.merchant_name" {
+				if _, ok := seen["merchant.name"]; ok {
+					continue
+				}
+			}
 			if _, ok := seen[tf]; ok {
 				continue
 			}