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/__tests__/SearchExtraToolsHint.test.ts

@@ -0,0 +1,82 @@
+import { describe, test, expect, beforeEach } from 'bun:test'
+import { mock } from 'bun:test'
+import { logMock } from '../../../tests/mocks/log'
+import { debugMock } from '../../../tests/mocks/debug'
+
+mock.module('src/utils/log.ts', logMock)
+mock.module('src/utils/debug.ts', debugMock)
+mock.module('src/services/analytics/growthbook.js', () => ({
+  getFeatureValue_CACHED_MAY_BE_STALE: () => false,
+  checkStatsigFeatureGate_CACHED_MAY_BE_STALE: () => false,
+  getFeatureValue_DEPRECATED: async () => undefined,
+  getFeatureValue_CACHED_WITH_REFRESH: async () => undefined,
+  hasGrowthBookEnvOverride: () => false,
+  getAllGrowthBookFeatures: () => ({}),
+  getGrowthBookConfigOverrides: () => ({}),
+  setGrowthBookConfigOverride: () => {},
+  clearGrowthBookConfigOverrides: () => {},
+  getApiBaseUrlHost: () => undefined,
+  onGrowthBookRefresh: () => {},
+  initializeGrowthBook: async () => {},
+  checkSecurityRestrictionGate: async () => false,
+  checkGate_CACHED_OR_BLOCKING: async () => false,
+  refreshGrowthBookAfterAuthChange: () => {},
+  resetGrowthBook: () => {},
+  refreshGrowthBookFeatures: async () => {},
+  setupPeriodicGrowthBookRefresh: () => {},
+  stopPeriodicGrowthBookRefresh: () => {},
+  getDynamicConfig_CACHED_MAY_BE_STALE: () => undefined,
+  getDynamicConfig_BLOCKS_ON_INIT: async () => undefined,
+}))
+
+const {
+  subscribeToSearchExtraToolsPrefetch,
+  getSearchExtraToolsPrefetchSnapshot,
+  clearSearchExtraToolsPrefetchResults,
+} = await import('src/services/searchExtraTools/prefetch.js')
+
+const { useSearchExtraToolsHint } = await import(
+  'src/hooks/useSearchExtraToolsHint.js'
+)
+
+describe('useSearchExtraToolsHint', () => {
+  // We test the subscription/snapshot API directly since
+  // React hooks require a renderer.
+  test('returns empty tools when no prefetch result', () => {
+    clearSearchExtraToolsPrefetchResults()
+    const snapshot = getSearchExtraToolsPrefetchSnapshot()
+    expect(snapshot).toEqual([])
+  })
+
+  test('snapshot updates when listeners are notified', () => {
+    clearSearchExtraToolsPrefetchResults()
+
+    // Simulate what prefetch does: set results and notify
+    const mockSetResults = (results: unknown[]) => {
+      // We can't directly set latestPrefetchResult, but we can test
+      // the clear function and subscription mechanism
+      clearSearchExtraToolsPrefetchResults()
+    }
+
+    // Test subscription
+    let callCount = 0
+    const unsubscribe = subscribeToSearchExtraToolsPrefetch(() => {
+      callCount++
+    })
+    expect(callCount).toBe(0)
+
+    // Trigger a notification via clear
+    mockSetResults([])
+    expect(callCount).toBe(1)
+
+    // Unsubscribe and verify no more calls
+    unsubscribe()
+    clearSearchExtraToolsPrefetchResults()
+    expect(callCount).toBe(1)
+  })
+
+  test('clearSearchExtraToolsPrefetchResults resets snapshot', () => {
+    clearSearchExtraToolsPrefetchResults()
+    expect(getSearchExtraToolsPrefetchSnapshot()).toEqual([])
+  })
+})