feat: Agent 支持 etcdctl/etcdutl 诊断命令

etcd 是 K8S 控制平面的关键组件，缺少 etcd 诊断会导致很多故障无法
继续排查。本次将 etcdctl 和 etcdutl 纳入命令白名单：

只读 (自动执行):
- etcdctl endpoint status/health/hashkv - 端点健康
- etcdctl member list - 成员列表
- etcdctl alarm list - 告警
- etcdctl auth/user/role status|list - 认证与权限查看
- etcdctl check perf/datascale - 性能检查
- etcdctl get/watch - 读取 key
- etcdctl version
- etcdutl snapshot status/hash - 快照检查
- etcdutl version

写操作 (人工审批):
- etcdctl put/del/compact/txn - 数据修改
- etcdctl snapshot save - 保存快照
- etcdctl member add/remove/update - 成员管理
- etcdctl alarm disarm - 解除告警
- etcdctl auth enable/disable - 认证开关
- etcdctl user/role add/delete/grant/revoke - 权限管理
- etcdutl snapshot restore - 恢复快照

实现细节:
- etcdctl/etcdutl 命令支持全局 flag (--endpoints/--cacert 等在子命令前)
- 两段式命令按 (verb, subverb) 组合精确分类，避免 member list (只读)
  和 member remove (写) 混淆
- 新增 12 个 etcd 命令分类测试，全部 56 个测试通过

tests/test_agent_tools.py

@@ -102,6 +102,71 @@ class ShellCommandPolicyTest(unittest.TestCase):
             classify_shell_command("cat /etc/shadow")
 
 
+class EtcdCommandPolicyTest(unittest.TestCase):
+    def test_etcdctl_endpoint_status_is_read_only(self):
+        decision = classify_shell_command("etcdctl endpoint status")
+        self.assertEqual(decision.mode, "read")
+        self.assertFalse(decision.requires_approval)
+
+    def test_etcdctl_with_global_flags_still_classifies(self):
+        decision = classify_shell_command(
+            "etcdctl --endpoints=https://127.0.0.1:2379 --cacert=/etc/ssl/ca.pem endpoint health"
+        )
+        self.assertEqual(decision.mode, "read")
+        self.assertFalse(decision.requires_approval)
+
+    def test_etcdctl_member_list_is_read_only(self):
+        decision = classify_shell_command("etcdctl member list")
+        self.assertEqual(decision.mode, "read")
+        self.assertFalse(decision.requires_approval)
+
+    def test_etcdctl_get_and_version_are_read_only(self):
+        for command in ("etcdctl get /kubernetes", "etcdctl version", "etcdctl alarm list"):
+            with self.subTest(command=command):
+                decision = classify_shell_command(command)
+                self.assertEqual(decision.mode, "read")
+                self.assertFalse(decision.requires_approval)
+
+    def test_etcdutl_snapshot_status_is_read_only(self):
+        decision = classify_shell_command("etcdutl snapshot status /tmp/etcd.db")
+        self.assertEqual(decision.mode, "read")
+        self.assertFalse(decision.requires_approval)
+
+    def test_etcdctl_put_requires_approval(self):
+        decision = classify_shell_command("etcdctl put key value")
+        self.assertEqual(decision.mode, "write")
+        self.assertTrue(decision.requires_approval)
+
+    def test_etcdctl_member_remove_requires_approval(self):
+        decision = classify_shell_command("etcdctl member remove abc123")
+        self.assertEqual(decision.mode, "write")
+        self.assertTrue(decision.requires_approval)
+
+    def test_etcdctl_snapshot_save_requires_approval(self):
+        decision = classify_shell_command("etcdctl snapshot save /tmp/etcd.db")
+        self.assertEqual(decision.mode, "write")
+        self.assertTrue(decision.requires_approval)
+
+    def test_etcdctl_compact_requires_approval(self):
+        decision = classify_shell_command("etcdctl compact 12345")
+        self.assertEqual(decision.mode, "write")
+        self.assertTrue(decision.requires_approval)
+
+    def test_etcdctl_auth_enable_requires_approval(self):
+        decision = classify_shell_command("etcdctl auth enable")
+        self.assertEqual(decision.mode, "write")
+        self.assertTrue(decision.requires_approval)
+
+    def test_etcdutl_snapshot_restore_requires_approval(self):
+        decision = classify_shell_command("etcdutl snapshot restore /tmp/etcd.db")
+        self.assertEqual(decision.mode, "write")
+        self.assertTrue(decision.requires_approval)
+
+    def test_etcdctl_rejects_unknown_subcommand(self):
+        with self.assertRaises(ValueError):
+            classify_shell_command("etcdctl bogus command")
+
+
 class AgentCommandDispatchTest(unittest.TestCase):
     def test_dispatches_kubectl_command_to_kubectl_classifier(self):
         decision = classify_agent_command("kubectl get pods -A")