docs: 添加 ToolSearch 设计指南 + 禁用 turn-zero 工具推荐弹窗

- 新增 docs/design/tool-search-design-guide.md，涵盖架构、搜索算法、执行管道、演进历史
- 禁用 getTurnZeroSearchExtraToolsPrefetch，消除用户输入时的频繁弹窗
- inter-turn 发现机制保持不变

Co-Authored-By: glm-5-turbo <zai-org@claude-code-best.win>

src/Tool.ts

@@ -391,7 +391,7 @@ export type Tool<
    */
   aliases?: string[]
   /**
-   * One-line capability phrase used by ToolSearch for keyword matching.
+   * One-line capability phrase used by SearchExtraTools for keyword matching.
    * Helps the model find this tool via keyword search when it's deferred.
    * 3–10 words, no trailing period.
    * Prefer terms not already in the tool name (e.g. 'jupyter' for NotebookEdit).
@@ -458,14 +458,14 @@ export type Tool<
   isLsp?: boolean
   /**
    * When true, this tool is deferred (sent with defer_loading: true) and requires
-   * ToolSearch to be used before it can be called.
+   * SearchExtraTools to be used before it can be called.
    */
   readonly shouldDefer?: boolean
   /**
    * When true, this tool is never deferred — its full schema appears in the
-   * initial prompt even when ToolSearch is enabled. For MCP tools, set via
+   * initial prompt even when SearchExtraTools is enabled. For MCP tools, set via
    * `_meta['anthropic/alwaysLoad']`. Use for tools the model must see on
-   * turn 1 without a ToolSearch round-trip.
+   * turn 1 without a SearchExtraTools round-trip.
    */
   readonly alwaysLoad?: boolean
   /**