feat(history): make query history retention configurable

docs/content/docs/query-editor.cn.mdx

@@ -141,6 +141,8 @@ description: 使用 DBX 编写、理解、参数化、执行、分析和复用 S
 
 ## 查询历史
 
+在 **设置 → 数据 → 查询历史保留条数** 中，可选择 **200**、**1000**（默认）、**5000**、**10000** 或 **不限**。上限由所有连接及执行来源（包括 MCP）共用。调小后，下次记录历史时才会删除超出上限的旧记录；提高上限不会恢复已删除的记录。历史分页大小保持不变。
+
 查询历史按连接保存已执行 SQL，并记录时间和相关上下文。可以：
 
 - 按日期范围过滤

docs/content/docs/query-editor.mdx

@@ -141,6 +141,8 @@ Explain Plan accepts query-like SQL that is safe to analyze, such as `SELECT`, `
 
 ## Query History
 
+In **Settings → Data → Query history retention**, choose **200**, **1000** (default), **5000**, **10000**, or **Unlimited**. The limit is shared by all connections and execution sources, including MCP. A lower limit takes effect the next time a history entry is recorded: older entries beyond the limit are deleted. Raising the limit does not recover deleted entries. History page sizes remain unchanged.
+
 Query history stores executed SQL per connection with time and context. You can:
 
 - Filter by date range