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/utils/messages.ts

@@ -3909,7 +3909,24 @@ Read the team config to discover your teammates' names. Check the task list peri
     }
   }
 
-  // eslint-disable-next-line @typescript-eslint/switch-exhaustiveness-check -- teammate_mailbox/team_context/skill_discovery/bagel_console handled above
+  // tool_discovery handled here (not in the switch) so the 'tool_discovery'
+  // string literal lives inside a feature()-guarded block.
+  if (feature('EXPERIMENTAL_TOOL_SEARCH')) {
+    if (attachment.type === 'tool_discovery') {
+      if (attachment.tools.length === 0) return []
+      const lines = attachment.tools.map(
+        t => `- ${t.name}: ${t.description.slice(0, 100)}`,
+      )
+      return wrapMessagesInSystemReminder([
+        createUserMessage({
+          content: `The following tools were discovered as relevant to your task. Use ExecuteTool to invoke any of them by name:\n\n${lines.join('\n')}`,
+          isMeta: true,
+        }),
+      ])
+    }
+  }
+
+  // eslint-disable-next-line @typescript-eslint/switch-exhaustiveness-check -- teammate_mailbox/team_context/skill_discovery/tool_discovery/bagel_console handled above
   switch (attachment.type) {
     case 'directory': {
       return wrapMessagesInSystemReminder([