feat: 实现 Tool Search 基础设施层（CORE_TOOLS 白名单 + TF-IDF 索引 + ExecuteTool + 搜索增强）

- 新增 CORE_TOOLS 白名单常量（31 个核心工具），重构 isDeferredTool 为白名单制判定
- 新建 TF-IDF 工具索引模块（toolIndex.ts），复用 localSearch.ts 算法函数
- 新建 ExecuteTool 跨 API provider 统一工具执行入口
- 增强 ToolSearchTool：TF-IDF 搜索路径、discover: 模式、并行搜索合并、文本模式回退
- 新增 27 个单元测试，precheck 零错误通过（4108 tests pass）

Co-Authored-By: glm-5.1[1m] <zai-org@claude-code-best.win>

src/hooks/useToolSearchHint.ts

@@ -0,0 +1,53 @@
+import * as React from 'react'
+import {
+  subscribeToToolSearchPrefetch,
+  getToolSearchPrefetchSnapshot,
+  clearToolSearchPrefetchResults,
+  type ToolDiscoveryResult,
+} from 'src/services/toolSearch/prefetch.js'
+
+type ToolSearchHintItem = {
+  name: string
+  description: string
+  score: number
+}
+
+type ToolSearchHintResult = {
+  tools: ToolSearchHintItem[]
+  visible: boolean
+  handleSelect: (toolName: string) => void
+  handleDismiss: () => void
+}
+
+const MAX_HINT_SCORE = 0.15
+const MAX_HINT_TOOLS = 3
+
+export function useToolSearchHint(): ToolSearchHintResult {
+  const prefetchResult = React.useSyncExternalStore(
+    subscribeToToolSearchPrefetch,
+    getToolSearchPrefetchSnapshot,
+  )
+
+  const tools: ToolSearchHintItem[] = React.useMemo(() => {
+    if (prefetchResult.length === 0) return []
+    return prefetchResult
+      .slice(0, MAX_HINT_TOOLS)
+      .map((r: ToolDiscoveryResult) => ({
+        name: r.name,
+        description: r.description.slice(0, 60),
+        score: r.score,
+      }))
+  }, [prefetchResult])
+
+  const visible = tools.length > 0 && (tools[0]?.score ?? 0) >= MAX_HINT_SCORE
+
+  const handleSelect = React.useCallback((_toolName: string) => {
+    clearToolSearchPrefetchResults()
+  }, [])
+
+  const handleDismiss = React.useCallback(() => {
+    clearToolSearchPrefetchResults()
+  }, [])
+
+  return { tools, visible, handleSelect, handleDismiss }
+}