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/components/Messages.tsx

@@ -852,7 +852,7 @@ const MessagesImpl = ({
   // renderToolResultMessage shows. Falls back to renderableSearchText
   // (duck-types toolUseResult) for tools that haven't implemented it,
   // and for all non-tool-result message types. The drift-catcher test
-  // (toolSearchText.test.tsx) renders + compares to keep these in sync.
+  // (searchExtraToolsText.test.tsx) renders + compares to keep these in sync.
   //
   // A second-React-root reconcile approach was tried and ruled out
   // (measured 3.1ms/msg, growing — flushSyncWork processes all roots;