feat(api): 优化字段去重逻辑并添加标签去重处理

在exports.go中增强字段去重逻辑，确保主表字段优先于副表字段，并处理相同列名的去重，提升导出数据的准确性和一致性。同时，添加字段匹配校验以确保最终字段数量与模板一致。

server/internal/api/exports.go

@@ -300,6 +300,44 @@ func (a *ExportsAPI) create(w http.ResponseWriter, r *http.Request) {
 			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
+	{
+		labelIdx := map[string]int{}
+		deduped := make([]string, 0, len(filtered))
+		removed := []string{}
+		for _, tf := range filtered {
+			label := labels[tf]
+			if label == "" {
+				label = tf
+			}
+			parts := strings.Split(tf, ".")
+			isMain := len(parts) == 2 && parts[0] == main
+			if idx, ok := labelIdx[label]; ok {
+				prev := deduped[idx]
+				prevParts := strings.Split(prev, ".")
+				prevMain := len(prevParts) == 2 && prevParts[0] == main
+				switch {
+				case prevMain:
+					removed = append(removed, tf)
+					continue
+				case isMain:
+					removed = append(removed, prev)
+					deduped[idx] = tf
+					continue
+				default:
+					removed = append(removed, tf)
+					continue
+				}
+			}
+			labelIdx[label] = len(deduped)
+			deduped = append(deduped, tf)
+		}
+		if len(removed) > 0 {
+			logging.JSON("INFO", map[string]interface{}{"event": "fields_deduplicated_by_label", "removed": removed, "reason": "同名列优先保留主表字段"})
+		}
+		filtered = deduped
+	}
 	// 字段匹配校验（数量与顺序）
 	if len(filtered) != len(fs) {
 		logging.JSON("ERROR", map[string]interface{}{"event": "field_count_mismatch", "template_count": len(fs), "final_count": len(filtered)})
@@ -329,7 +367,6 @@ func (a *ExportsAPI) create(w http.ResponseWriter, r *http.Request) {
 	}
 	var estimate int64
 	estimate = rrepo.EstimateFastChunked(dataDB, ds, main, p.Filters)
-	labels := FieldLabels()
 	hdrs := make([]string, len(filtered))
 	for i, tf := range filtered {
 		if v, ok := labels[tf]; ok {
@@ -347,7 +384,7 @@ func (a *ExportsAPI) create(w http.ResponseWriter, r *http.Request) {
 		for i := range hdrs {
 			if cnt[hdrs[i]] > 1 {
 				parts := strings.Split(filtered[i], ".")
-				if len(parts) == 2 && parts[0] != "order" {
+				if len(parts) == 2 && parts[0] != main {
 					hdrs[i] = tableLabel(parts[0]) + "." + hdrs[i]
 				}
 			}