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/services/acp/__tests__/bridge.test.ts

@@ -482,7 +482,7 @@ describe('toolUpdateFromToolResult', () => {
         is_error: false,
         tool_use_id: 't1',
       },
-      { name: 'ToolSearch', id: 't1' },
+      { name: 'SearchExtraTools', id: 't1' },
     )
     expect(result.content).toEqual([
       { type: 'content', content: { type: 'text', text: 'Tool: some_tool' } },