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>

packages/builtin-tools/src/tools/ExecuteTool/ExecuteTool.ts

@@ -68,7 +68,7 @@ export const ExecuteTool = buildTool({
         },
         newMessages: [
           createUserMessage({
-            content: `Tool "${input.tool_name}" not found. Use ToolSearch to discover available tools.`,
+            content: `Tool "${input.tool_name}" not found. Use SearchExtraTools to discover available tools.`,
           }),
         ],
       }