重构：简化查询接口

- RecordQuery.QueryOldest 和 QueryNewest 不再接收 startIdx/endIdx 参数
- 查询方法返回纯 Record 列表，状态判断移到调用方
- TopicProcessor 的查询方法负责添加状态信息
- 更新所有测试文件以适配新接口

example/webapp/main.go

@@ -541,47 +541,30 @@ func handleQuery(w http.ResponseWriter, r *http.Request) {
 	startIdx := seq.GetProcessingIndex(topic)
 	endIdx := seq.GetReadIndex(topic)
 
-	// 获取索引用于转换
-	processor, err := seq.GetProcessor(topic)
-	if err != nil {
-		http.Error(w, err.Error(), http.StatusNotFound)
-		return
-	}
-	index := processor.Index()
-
 	// 合并查询结果：向后 + 当前 + 向前
 	var results []*seqlog.RecordWithStatus
 
 	// 向后查询
 	if backward > 0 && startIdx > 0 {
-		startPos, err := index.GetOffset(startIdx)
+		backResults, err := query.QueryNewest(startIdx-1, backward, startIdx, endIdx)
 		if err == nil {
-			backResults, err := query.QueryAt(startPos, -1, backward, startIdx, endIdx)
-			if err == nil {
-				results = append(results, backResults...)
-			}
+			results = append(results, backResults...)
 		}
 	}
 
 	// 当前位置
 	if startIdx < endIdx {
-		startPos, err := index.GetOffset(startIdx)
+		currentResults, err := query.QueryOldest(startIdx, 1, startIdx, endIdx)
 		if err == nil {
-			currentResults, err := query.QueryAt(startPos, 0, 1, startIdx, endIdx)
-			if err == nil {
-				results = append(results, currentResults...)
-			}
+			results = append(results, currentResults...)
 		}
 	}
 
 	// 向前查询
 	if forward > 0 {
-		startPos, err := index.GetOffset(startIdx)
+		forwardResults, err := query.QueryOldest(endIdx, forward, startIdx, endIdx)
 		if err == nil {
-			forwardResults, err := query.QueryAt(startPos, 1, forward, startIdx, endIdx)
-			if err == nil {
-				results = append(results, forwardResults...)
-			}
+			results = append(results, forwardResults...)
 		}
 	}