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>

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

@@ -0,0 +1,16 @@
+import { EXECUTE_TOOL_NAME } from './constants.js'
+
+export const DESCRIPTION =
+  'Execute a deferred tool by name with parameters. Use this after discovering a tool via ToolSearch.'
+
+export function getPrompt(): string {
+  return `Execute a deferred tool by name. This tool accepts a tool_name and params object, looks up the target tool in the global tool registry, and delegates execution to it.
+
+Use this tool after discovering a deferred tool via ToolSearch. The tool_name must match the exact name returned by ToolSearch (e.g., "CronCreate", "mcp__server__action").
+
+Inputs:
+- tool_name: The exact name of the target tool (string)
+- params: The parameters to pass to the target tool (object)
+
+If the tool is not found, an error message will be returned suggesting to use ToolSearch to discover available tools.`
+}