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/constants/promptEngineeringAudit.runner.ts

@@ -663,7 +663,7 @@ describe('Opus 4.7 Prompt Engineering Audit', () => {
       const prompt = await getFullPrompt()
       expect(prompt).toContain('search for it')
       expect(prompt).toContain(
-        'Only state something is unavailable after ToolSearch returns no match',
+        'Only state something is unavailable after SearchExtraTools returns no match',
       )
     })